/*
 * Copyright (c) 1996, 2017, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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 * questions.
 */

package java.io;

import java.io.ObjectStreamClass.WeakClassKey;
import java.lang.ref.ReferenceQueue;
import java.security.AccessController;
import java.security.PrivilegedAction;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.StringJoiner;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentMap;
import static java.io.ObjectStreamClass.processQueue;
import sun.reflect.misc.ReflectUtil;

An ObjectOutputStream writes primitive data types and graphs of Java objects
to an OutputStream.  The objects can be read (reconstituted) using an
ObjectInputStream.  Persistent storage of objects can be accomplished by
using a file for the stream.  If the stream is a network socket stream, the
objects can be reconstituted on another host or in another process.
Only objects that support the java.io.Serializable interface can be
written to streams.  The class of each serializable object is encoded
including the class name and signature of the class, the values of the
object's fields and arrays, and the closure of any other objects referenced
from the initial objects.
The method writeObject is used to write an object to the stream.  Any
object, including Strings and arrays, is written with writeObject. Multiple
objects or primitives can be written to the stream.  The objects must be
read back from the corresponding ObjectInputstream with the same types and
in the same order as they were written.
Primitive data types can also be written to the stream using the
appropriate methods from DataOutput. Strings can also be written using the
writeUTF method.
The default serialization mechanism for an object writes the class of the
object, the class signature, and the values of all non-transient and
non-static fields.  References to other objects (except in transient or
static fields) cause those objects to be written also. Multiple references
to a single object are encoded using a reference sharing mechanism so that
graphs of objects can be restored to the same shape as when the original was
written.
For example to write an object that can be read by the example in
ObjectInputStream:


     FileOutputStream fos = new FileOutputStream("t.tmp");
     ObjectOutputStream oos = new ObjectOutputStream(fos);
     oos.writeInt(12345);
     oos.writeObject("Today");
     oos.writeObject(new Date());
     oos.close();

Classes that require special handling during the serialization and
deserialization process must implement special methods with these exact
signatures:


private void readObject(java.io.ObjectInputStream stream)
    throws IOException, ClassNotFoundException;
private void writeObject(java.io.ObjectOutputStream stream)
    throws IOException
private void readObjectNoData()
    throws ObjectStreamException;

The writeObject method is responsible for writing the state of the object
for its particular class so that the corresponding readObject method can
restore it.  The method does not need to concern itself with the state
belonging to the object's superclasses or subclasses.  State is saved by
writing the individual fields to the ObjectOutputStream using the
writeObject method or by using the methods for primitive data types
supported by DataOutput.
Serialization does not write out the fields of any object that does not
implement the java.io.Serializable interface.  Subclasses of Objects that
are not serializable can be serializable. In this case the non-serializable
class must have a no-arg constructor to allow its fields to be initialized.
In this case it is the responsibility of the subclass to save and restore
the state of the non-serializable class. It is frequently the case that the
fields of that class are accessible (public, package, or protected) or that
there are get and set methods that can be used to restore the state.
Serialization of an object can be prevented by implementing writeObject
and readObject methods that throw the NotSerializableException.  The
exception will be caught by the ObjectOutputStream and abort the
serialization process.
Implementing the Externalizable interface allows the object to assume
complete control over the contents and format of the object's serialized
form.  The methods of the Externalizable interface, writeExternal and
readExternal, are called to save and restore the objects state.  When
implemented by a class they can write and read their own state using all of
the methods of ObjectOutput and ObjectInput.  It is the responsibility of
the objects to handle any versioning that occurs.
Enum constants are serialized differently than ordinary serializable or
externalizable objects.  The serialized form of an enum constant consists
solely of its name; field values of the constant are not transmitted.  To
serialize an enum constant, ObjectOutputStream writes the string returned by
the constant's name method.  Like other serializable or externalizable
objects, enum constants can function as the targets of back references
appearing subsequently in the serialization stream.  The process by which
enum constants are serialized cannot be customized; any class-specific
writeObject and writeReplace methods defined by enum types are ignored
during serialization.  Similarly, any serialPersistentFields or
serialVersionUID field declarations are also ignored--all enum types have a
fixed serialVersionUID of 0L.
Primitive data, excluding serializable fields and externalizable data, is
written to the ObjectOutputStream in block-data records. A block data record
is composed of a header and data. The block data header consists of a marker
and the number of bytes to follow the header.  Consecutive primitive data
writes are merged into one block-data record.  The blocking factor used for
a block-data record will be 1024 bytes.  Each block-data record will be
filled up to 1024 bytes, or be written whenever there is a termination of
block-data mode.  Calls to the ObjectOutputStream methods writeObject,
defaultWriteObject and writeFields initially terminate any existing
block-data record.
Author:
     Mike Warres,      Roger Riggs
See Also:
DataOutput
ObjectInputStream
Serializable
Externalizable

 *     Object Serialization Specification, Section 2, Object Output Classes
Since:
      1.1/**
 * An ObjectOutputStream writes primitive data types and graphs of Java objects
 * to an OutputStream.  The objects can be read (reconstituted) using an
 * ObjectInputStream.  Persistent storage of objects can be accomplished by
 * using a file for the stream.  If the stream is a network socket stream, the
 * objects can be reconstituted on another host or in another process.
 *
 * <p>Only objects that support the java.io.Serializable interface can be
 * written to streams.  The class of each serializable object is encoded
 * including the class name and signature of the class, the values of the
 * object's fields and arrays, and the closure of any other objects referenced
 * from the initial objects.
 *
 * <p>The method writeObject is used to write an object to the stream.  Any
 * object, including Strings and arrays, is written with writeObject. Multiple
 * objects or primitives can be written to the stream.  The objects must be
 * read back from the corresponding ObjectInputstream with the same types and
 * in the same order as they were written.
 *
 * <p>Primitive data types can also be written to the stream using the
 * appropriate methods from DataOutput. Strings can also be written using the
 * writeUTF method.
 *
 * <p>The default serialization mechanism for an object writes the class of the
 * object, the class signature, and the values of all non-transient and
 * non-static fields.  References to other objects (except in transient or
 * static fields) cause those objects to be written also. Multiple references
 * to a single object are encoded using a reference sharing mechanism so that
 * graphs of objects can be restored to the same shape as when the original was
 * written.
 *
 * <p>For example to write an object that can be read by the example in
 * ObjectInputStream:
 * <br>
 * <pre>
 *      FileOutputStream fos = new FileOutputStream("t.tmp");
 *      ObjectOutputStream oos = new ObjectOutputStream(fos);
 *
 *      oos.writeInt(12345);
 *      oos.writeObject("Today");
 *      oos.writeObject(new Date());
 *
 *      oos.close();
 * </pre>
 *
 * <p>Classes that require special handling during the serialization and
 * deserialization process must implement special methods with these exact
 * signatures:
 * <br>
 * <pre>
 * private void readObject(java.io.ObjectInputStream stream)
 *     throws IOException, ClassNotFoundException;
 * private void writeObject(java.io.ObjectOutputStream stream)
 *     throws IOException
 * private void readObjectNoData()
 *     throws ObjectStreamException;
 * </pre>
 *
 * <p>The writeObject method is responsible for writing the state of the object
 * for its particular class so that the corresponding readObject method can
 * restore it.  The method does not need to concern itself with the state
 * belonging to the object's superclasses or subclasses.  State is saved by
 * writing the individual fields to the ObjectOutputStream using the
 * writeObject method or by using the methods for primitive data types
 * supported by DataOutput.
 *
 * <p>Serialization does not write out the fields of any object that does not
 * implement the java.io.Serializable interface.  Subclasses of Objects that
 * are not serializable can be serializable. In this case the non-serializable
 * class must have a no-arg constructor to allow its fields to be initialized.
 * In this case it is the responsibility of the subclass to save and restore
 * the state of the non-serializable class. It is frequently the case that the
 * fields of that class are accessible (public, package, or protected) or that
 * there are get and set methods that can be used to restore the state.
 *
 * <p>Serialization of an object can be prevented by implementing writeObject
 * and readObject methods that throw the NotSerializableException.  The
 * exception will be caught by the ObjectOutputStream and abort the
 * serialization process.
 *
 * <p>Implementing the Externalizable interface allows the object to assume
 * complete control over the contents and format of the object's serialized
 * form.  The methods of the Externalizable interface, writeExternal and
 * readExternal, are called to save and restore the objects state.  When
 * implemented by a class they can write and read their own state using all of
 * the methods of ObjectOutput and ObjectInput.  It is the responsibility of
 * the objects to handle any versioning that occurs.
 *
 * <p>Enum constants are serialized differently than ordinary serializable or
 * externalizable objects.  The serialized form of an enum constant consists
 * solely of its name; field values of the constant are not transmitted.  To
 * serialize an enum constant, ObjectOutputStream writes the string returned by
 * the constant's name method.  Like other serializable or externalizable
 * objects, enum constants can function as the targets of back references
 * appearing subsequently in the serialization stream.  The process by which
 * enum constants are serialized cannot be customized; any class-specific
 * writeObject and writeReplace methods defined by enum types are ignored
 * during serialization.  Similarly, any serialPersistentFields or
 * serialVersionUID field declarations are also ignored--all enum types have a
 * fixed serialVersionUID of 0L.
 *
 * <p>Primitive data, excluding serializable fields and externalizable data, is
 * written to the ObjectOutputStream in block-data records. A block data record
 * is composed of a header and data. The block data header consists of a marker
 * and the number of bytes to follow the header.  Consecutive primitive data
 * writes are merged into one block-data record.  The blocking factor used for
 * a block-data record will be 1024 bytes.  Each block-data record will be
 * filled up to 1024 bytes, or be written whenever there is a termination of
 * block-data mode.  Calls to the ObjectOutputStream methods writeObject,
 * defaultWriteObject and writeFields initially terminate any existing
 * block-data record.
 *
 * @author      Mike Warres
 * @author      Roger Riggs
 * @see java.io.DataOutput
 * @see java.io.ObjectInputStream
 * @see java.io.Serializable
 * @see java.io.Externalizable
 * @see <a href="{@docRoot}/../specs/serialization/output.html">
 *     Object Serialization Specification, Section 2, Object Output Classes</a>
 * @since       1.1
 */
public class ObjectOutputStream
    extends OutputStream implements ObjectOutput, ObjectStreamConstants
{

    private static class Caches {
        
cache of subclass security audit results /** cache of subclass security audit results */
        static final ConcurrentMap<WeakClassKey,Boolean> subclassAudits =
            new ConcurrentHashMap<>();

        
queue for WeakReferences to audited subclasses /** queue for WeakReferences to audited subclasses */
        static final ReferenceQueue<Class<?>> subclassAuditsQueue =
            new ReferenceQueue<>();
    }

    
filter stream for handling block data conversion /** filter stream for handling block data conversion */
    private final BlockDataOutputStream bout;
    
obj -> wire handle map /** obj -> wire handle map */
    private final HandleTable handles;
    
obj -> replacement obj map /** obj -> replacement obj map */
    private final ReplaceTable subs;
    
stream protocol version /** stream protocol version */
    private int protocol = PROTOCOL_VERSION_2;
    
recursion depth /** recursion depth */
    private int depth;

    
buffer for writing primitive field values /** buffer for writing primitive field values */
    private byte[] primVals;

    
if true, invoke writeObjectOverride() instead of writeObject() /** if true, invoke writeObjectOverride() instead of writeObject() */
    private final boolean enableOverride;
    
if true, invoke replaceObject() /** if true, invoke replaceObject() */
    private boolean enableReplace;

    // values below valid only during upcalls to writeObject()/writeExternal()
    
Context during upcalls to class-defined writeObject methods; holds
object currently being serialized and descriptor for current class.
Null when not during writeObject upcall.
/**
     * Context during upcalls to class-defined writeObject methods; holds
     * object currently being serialized and descriptor for current class.
     * Null when not during writeObject upcall.
     */
    private SerialCallbackContext curContext;
    
current PutField object /** current PutField object */
    private PutFieldImpl curPut;

    
custom storage for debug trace info /** custom storage for debug trace info */
    private final DebugTraceInfoStack debugInfoStack;

    
value of "sun.io.serialization.extendedDebugInfo" property,
as true or false for extended information about exception's place
/**
     * value of "sun.io.serialization.extendedDebugInfo" property,
     * as true or false for extended information about exception's place
     */
    private static final boolean extendedDebugInfo =
        java.security.AccessController.doPrivileged(
            new sun.security.action.GetBooleanAction(
                "sun.io.serialization.extendedDebugInfo")).booleanValue();

    
Creates an ObjectOutputStream that writes to the specified OutputStream.
This constructor writes the serialization stream header to the
underlying stream; callers may wish to flush the stream immediately to
ensure that constructors for receiving ObjectInputStreams will not block
when reading the header.
If a security manager is installed, this constructor will check for
the "enableSubclassImplementation" SerializablePermission when invoked
directly or indirectly by the constructor of a subclass which overrides
the ObjectOutputStream.putFields or ObjectOutputStream.writeUnshared
methods.
Params:
out – output stream to write to
Throws:
IOException – if an I/O error occurs while writing stream header
SecurityException – if untrusted subclass illegally overrides
         security-sensitive methods
NullPointerException – if out is null
See Also:
ObjectOutputStream()
putFields()
ObjectInputStream(InputStream)
Since:
  1.4/**
     * Creates an ObjectOutputStream that writes to the specified OutputStream.
     * This constructor writes the serialization stream header to the
     * underlying stream; callers may wish to flush the stream immediately to
     * ensure that constructors for receiving ObjectInputStreams will not block
     * when reading the header.
     *
     * <p>If a security manager is installed, this constructor will check for
     * the "enableSubclassImplementation" SerializablePermission when invoked
     * directly or indirectly by the constructor of a subclass which overrides
     * the ObjectOutputStream.putFields or ObjectOutputStream.writeUnshared
     * methods.
     *
     * @param   out output stream to write to
     * @throws  IOException if an I/O error occurs while writing stream header
     * @throws  SecurityException if untrusted subclass illegally overrides
     *          security-sensitive methods
     * @throws  NullPointerException if <code>out</code> is <code>null</code>
     * @since   1.4
     * @see     ObjectOutputStream#ObjectOutputStream()
     * @see     ObjectOutputStream#putFields()
     * @see     ObjectInputStream#ObjectInputStream(InputStream)
     */
    public ObjectOutputStream(OutputStream out) throws IOException {
        verifySubclass();
        bout = new BlockDataOutputStream(out);
        handles = new HandleTable(10, (float) 3.00);
        subs = new ReplaceTable(10, (float) 3.00);
        enableOverride = false;
        writeStreamHeader();
        bout.setBlockDataMode(true);
        if (extendedDebugInfo) {
            debugInfoStack = new DebugTraceInfoStack();
        } else {
            debugInfoStack = null;
        }
    }

    
Provide a way for subclasses that are completely reimplementing
ObjectOutputStream to not have to allocate private data just used by
this implementation of ObjectOutputStream.
If there is a security manager installed, this method first calls the
security manager's checkPermission method with a
SerializablePermission("enableSubclassImplementation")
permission to ensure it's ok to enable subclassing.
Throws:
SecurityException – if a security manager exists and its
         checkPermission method denies enabling
         subclassing.
IOException – if an I/O error occurs while creating this stream
See Also:
SecurityManager.checkPermission
SerializablePermission/**
     * Provide a way for subclasses that are completely reimplementing
     * ObjectOutputStream to not have to allocate private data just used by
     * this implementation of ObjectOutputStream.
     *
     * <p>If there is a security manager installed, this method first calls the
     * security manager's <code>checkPermission</code> method with a
     * <code>SerializablePermission("enableSubclassImplementation")</code>
     * permission to ensure it's ok to enable subclassing.
     *
     * @throws  SecurityException if a security manager exists and its
     *          <code>checkPermission</code> method denies enabling
     *          subclassing.
     * @throws  IOException if an I/O error occurs while creating this stream
     * @see SecurityManager#checkPermission
     * @see java.io.SerializablePermission
     */
    protected ObjectOutputStream() throws IOException, SecurityException {
        SecurityManager sm = System.getSecurityManager();
        if (sm != null) {
            sm.checkPermission(SUBCLASS_IMPLEMENTATION_PERMISSION);
        }
        bout = null;
        handles = null;
        subs = null;
        enableOverride = true;
        debugInfoStack = null;
    }

    
Specify stream protocol version to use when writing the stream.
This routine provides a hook to enable the current version of
Serialization to write in a format that is backwards compatible to a
previous version of the stream format.
Every effort will be made to avoid introducing additional
backwards incompatibilities; however, sometimes there is no
other alternative.
Params:
version – use ProtocolVersion from java.io.ObjectStreamConstants.
Throws:
IllegalStateException – if called after any objects
         have been serialized.
IllegalArgumentException – if invalid version is passed in.
IOException – if I/O errors occur
See Also:
ObjectStreamConstants.PROTOCOL_VERSION_1
ObjectStreamConstants.PROTOCOL_VERSION_2
Since:
  1.2/**
     * Specify stream protocol version to use when writing the stream.
     *
     * <p>This routine provides a hook to enable the current version of
     * Serialization to write in a format that is backwards compatible to a
     * previous version of the stream format.
     *
     * <p>Every effort will be made to avoid introducing additional
     * backwards incompatibilities; however, sometimes there is no
     * other alternative.
     *
     * @param   version use ProtocolVersion from java.io.ObjectStreamConstants.
     * @throws  IllegalStateException if called after any objects
     *          have been serialized.
     * @throws  IllegalArgumentException if invalid version is passed in.
     * @throws  IOException if I/O errors occur
     * @see java.io.ObjectStreamConstants#PROTOCOL_VERSION_1
     * @see java.io.ObjectStreamConstants#PROTOCOL_VERSION_2
     * @since   1.2
     */
    public void useProtocolVersion(int version) throws IOException {
        if (handles.size() != 0) {
            // REMIND: implement better check for pristine stream?
            throw new IllegalStateException("stream non-empty");
        }
        switch (version) {
            case PROTOCOL_VERSION_1:
            case PROTOCOL_VERSION_2:
                protocol = version;
                break;

            default:
                throw new IllegalArgumentException(
                    "unknown version: " + version);
        }
    }

    
Write the specified object to the ObjectOutputStream.  The class of the
object, the signature of the class, and the values of the non-transient
and non-static fields of the class and all of its supertypes are
written.  Default serialization for a class can be overridden using the
writeObject and the readObject methods.  Objects referenced by this
object are written transitively so that a complete equivalent graph of
objects can be reconstructed by an ObjectInputStream.
Exceptions are thrown for problems with the OutputStream and for
classes that should not be serialized.  All exceptions are fatal to the
OutputStream, which is left in an indeterminate state, and it is up to
the caller to ignore or recover the stream state.
Throws:
InvalidClassException – Something is wrong with a class used by
         serialization.
NotSerializableException – Some object to be serialized does not
         implement the java.io.Serializable interface.
IOException – Any exception thrown by the underlying
         OutputStream./**
     * Write the specified object to the ObjectOutputStream.  The class of the
     * object, the signature of the class, and the values of the non-transient
     * and non-static fields of the class and all of its supertypes are
     * written.  Default serialization for a class can be overridden using the
     * writeObject and the readObject methods.  Objects referenced by this
     * object are written transitively so that a complete equivalent graph of
     * objects can be reconstructed by an ObjectInputStream.
     *
     * <p>Exceptions are thrown for problems with the OutputStream and for
     * classes that should not be serialized.  All exceptions are fatal to the
     * OutputStream, which is left in an indeterminate state, and it is up to
     * the caller to ignore or recover the stream state.
     *
     * @throws  InvalidClassException Something is wrong with a class used by
     *          serialization.
     * @throws  NotSerializableException Some object to be serialized does not
     *          implement the java.io.Serializable interface.
     * @throws  IOException Any exception thrown by the underlying
     *          OutputStream.
     */
    public final void writeObject(Object obj) throws IOException {
        if (enableOverride) {
            writeObjectOverride(obj);
            return;
        }
        try {
            writeObject0(obj, false);
        } catch (IOException ex) {
            if (depth == 0) {
                writeFatalException(ex);
            }
            throw ex;
        }
    }

    
Method used by subclasses to override the default writeObject method.
This method is called by trusted subclasses of ObjectInputStream that
constructed ObjectInputStream using the protected no-arg constructor.
The subclass is expected to provide an override method with the modifier
"final".
Params:
obj – object to be written to the underlying stream
Throws:
IOException – if there are I/O errors while writing to the
         underlying stream
See Also:
ObjectOutputStream()
writeObject(Object)
Since:
1.2/**
     * Method used by subclasses to override the default writeObject method.
     * This method is called by trusted subclasses of ObjectInputStream that
     * constructed ObjectInputStream using the protected no-arg constructor.
     * The subclass is expected to provide an override method with the modifier
     * "final".
     *
     * @param   obj object to be written to the underlying stream
     * @throws  IOException if there are I/O errors while writing to the
     *          underlying stream
     * @see #ObjectOutputStream()
     * @see #writeObject(Object)
     * @since 1.2
     */
    protected void writeObjectOverride(Object obj) throws IOException {
    }

    
Writes an "unshared" object to the ObjectOutputStream.  This method is
identical to writeObject, except that it always writes the given object
as a new, unique object in the stream (as opposed to a back-reference
pointing to a previously serialized instance).  Specifically:

  
An object written via writeUnshared is always serialized in the
      same manner as a newly appearing object (an object that has not
      been written to the stream yet), regardless of whether or not the
      object has been written previously.
  
If writeObject is used to write an object that has been previously
      written with writeUnshared, the previous writeUnshared operation
      is treated as if it were a write of a separate object.  In other
      words, ObjectOutputStream will never generate back-references to
      object data written by calls to writeUnshared.

While writing an object via writeUnshared does not in itself guarantee a
unique reference to the object when it is deserialized, it allows a
single object to be defined multiple times in a stream, so that multiple
calls to readUnshared by the receiver will not conflict.  Note that the
rules described above only apply to the base-level object written with
writeUnshared, and not to any transitively referenced sub-objects in the
object graph to be serialized.
ObjectOutputStream subclasses which override this method can only be
constructed in security contexts possessing the
"enableSubclassImplementation" SerializablePermission; any attempt to
instantiate such a subclass without this permission will cause a
SecurityException to be thrown.
Params:
obj – object to write to stream
Throws:
NotSerializableException – if an object in the graph to be
         serialized does not implement the Serializable interface
InvalidClassException – if a problem exists with the class of an
         object to be serialized
IOException – if an I/O error occurs during serialization
Since:
1.4/**
     * Writes an "unshared" object to the ObjectOutputStream.  This method is
     * identical to writeObject, except that it always writes the given object
     * as a new, unique object in the stream (as opposed to a back-reference
     * pointing to a previously serialized instance).  Specifically:
     * <ul>
     *   <li>An object written via writeUnshared is always serialized in the
     *       same manner as a newly appearing object (an object that has not
     *       been written to the stream yet), regardless of whether or not the
     *       object has been written previously.
     *
     *   <li>If writeObject is used to write an object that has been previously
     *       written with writeUnshared, the previous writeUnshared operation
     *       is treated as if it were a write of a separate object.  In other
     *       words, ObjectOutputStream will never generate back-references to
     *       object data written by calls to writeUnshared.
     * </ul>
     * While writing an object via writeUnshared does not in itself guarantee a
     * unique reference to the object when it is deserialized, it allows a
     * single object to be defined multiple times in a stream, so that multiple
     * calls to readUnshared by the receiver will not conflict.  Note that the
     * rules described above only apply to the base-level object written with
     * writeUnshared, and not to any transitively referenced sub-objects in the
     * object graph to be serialized.
     *
     * <p>ObjectOutputStream subclasses which override this method can only be
     * constructed in security contexts possessing the
     * "enableSubclassImplementation" SerializablePermission; any attempt to
     * instantiate such a subclass without this permission will cause a
     * SecurityException to be thrown.
     *
     * @param   obj object to write to stream
     * @throws  NotSerializableException if an object in the graph to be
     *          serialized does not implement the Serializable interface
     * @throws  InvalidClassException if a problem exists with the class of an
     *          object to be serialized
     * @throws  IOException if an I/O error occurs during serialization
     * @since 1.4
     */
    public void writeUnshared(Object obj) throws IOException {
        try {
            writeObject0(obj, true);
        } catch (IOException ex) {
            if (depth == 0) {
                writeFatalException(ex);
            }
            throw ex;
        }
    }

    
Write the non-static and non-transient fields of the current class to
this stream.  This may only be called from the writeObject method of the
class being serialized. It will throw the NotActiveException if it is
called otherwise.
Throws:
IOException – if I/O errors occur while writing to the underlying
         OutputStream/**
     * Write the non-static and non-transient fields of the current class to
     * this stream.  This may only be called from the writeObject method of the
     * class being serialized. It will throw the NotActiveException if it is
     * called otherwise.
     *
     * @throws  IOException if I/O errors occur while writing to the underlying
     *          <code>OutputStream</code>
     */
    public void defaultWriteObject() throws IOException {
        SerialCallbackContext ctx = curContext;
        if (ctx == null) {
            throw new NotActiveException("not in call to writeObject");
        }
        Object curObj = ctx.getObj();
        ObjectStreamClass curDesc = ctx.getDesc();
        bout.setBlockDataMode(false);
        defaultWriteFields(curObj, curDesc);
        bout.setBlockDataMode(true);
    }

    
Retrieve the object used to buffer persistent fields to be written to
the stream.  The fields will be written to the stream when writeFields
method is called.
Throws:
IOException – if I/O errors occur
Returns:
 an instance of the class Putfield that holds the serializable
         fields
Since:
1.2/**
     * Retrieve the object used to buffer persistent fields to be written to
     * the stream.  The fields will be written to the stream when writeFields
     * method is called.
     *
     * @return  an instance of the class Putfield that holds the serializable
     *          fields
     * @throws  IOException if I/O errors occur
     * @since 1.2
     */
    public ObjectOutputStream.PutField putFields() throws IOException {
        if (curPut == null) {
            SerialCallbackContext ctx = curContext;
            if (ctx == null) {
                throw new NotActiveException("not in call to writeObject");
            }
            ctx.checkAndSetUsed();
            ObjectStreamClass curDesc = ctx.getDesc();
            curPut = new PutFieldImpl(curDesc);
        }
        return curPut;
    }

    
Write the buffered fields to the stream.
Throws:
IOException – if I/O errors occur while writing to the underlying
         stream
NotActiveException – Called when a classes writeObject method was
         not called to write the state of the object.
Since:
1.2/**
     * Write the buffered fields to the stream.
     *
     * @throws  IOException if I/O errors occur while writing to the underlying
     *          stream
     * @throws  NotActiveException Called when a classes writeObject method was
     *          not called to write the state of the object.
     * @since 1.2
     */
    public void writeFields() throws IOException {
        if (curPut == null) {
            throw new NotActiveException("no current PutField object");
        }
        bout.setBlockDataMode(false);
        curPut.writeFields();
        bout.setBlockDataMode(true);
    }

    
Reset will disregard the state of any objects already written to the
stream.  The state is reset to be the same as a new ObjectOutputStream.
The current point in the stream is marked as reset so the corresponding
ObjectInputStream will be reset at the same point.  Objects previously
written to the stream will not be referred to as already being in the
stream.  They will be written to the stream again.
Throws:
IOException – if reset() is invoked while serializing an object./**
     * Reset will disregard the state of any objects already written to the
     * stream.  The state is reset to be the same as a new ObjectOutputStream.
     * The current point in the stream is marked as reset so the corresponding
     * ObjectInputStream will be reset at the same point.  Objects previously
     * written to the stream will not be referred to as already being in the
     * stream.  They will be written to the stream again.
     *
     * @throws  IOException if reset() is invoked while serializing an object.
     */
    public void reset() throws IOException {
        if (depth != 0) {
            throw new IOException("stream active");
        }
        bout.setBlockDataMode(false);
        bout.writeByte(TC_RESET);
        clear();
        bout.setBlockDataMode(true);
    }

    
Subclasses may implement this method to allow class data to be stored in
the stream. By default this method does nothing.  The corresponding
method in ObjectInputStream is resolveClass.  This method is called
exactly once for each unique class in the stream.  The class name and
signature will have already been written to the stream.  This method may
make free use of the ObjectOutputStream to save any representation of
the class it deems suitable (for example, the bytes of the class file).
The resolveClass method in the corresponding subclass of
ObjectInputStream must read and use any data or objects written by
annotateClass.
Params:
cl – the class to annotate custom data for
Throws:
IOException – Any exception thrown by the underlying
         OutputStream./**
     * Subclasses may implement this method to allow class data to be stored in
     * the stream. By default this method does nothing.  The corresponding
     * method in ObjectInputStream is resolveClass.  This method is called
     * exactly once for each unique class in the stream.  The class name and
     * signature will have already been written to the stream.  This method may
     * make free use of the ObjectOutputStream to save any representation of
     * the class it deems suitable (for example, the bytes of the class file).
     * The resolveClass method in the corresponding subclass of
     * ObjectInputStream must read and use any data or objects written by
     * annotateClass.
     *
     * @param   cl the class to annotate custom data for
     * @throws  IOException Any exception thrown by the underlying
     *          OutputStream.
     */
    protected void annotateClass(Class<?> cl) throws IOException {
    }

    
Subclasses may implement this method to store custom data in the stream
along with descriptors for dynamic proxy classes.
This method is called exactly once for each unique proxy class
descriptor in the stream.  The default implementation of this method in
ObjectOutputStream does nothing.
The corresponding method in ObjectInputStream is
resolveProxyClass.  For a given subclass of
ObjectOutputStream that overrides this method, the
resolveProxyClass method in the corresponding subclass of
ObjectInputStream must read any data or objects written by
annotateProxyClass.
Params:
cl – the proxy class to annotate custom data for
Throws:
IOException – any exception thrown by the underlying
         OutputStream
See Also:
ObjectInputStream.resolveProxyClass(String[])
Since:
  1.3/**
     * Subclasses may implement this method to store custom data in the stream
     * along with descriptors for dynamic proxy classes.
     *
     * <p>This method is called exactly once for each unique proxy class
     * descriptor in the stream.  The default implementation of this method in
     * <code>ObjectOutputStream</code> does nothing.
     *
     * <p>The corresponding method in <code>ObjectInputStream</code> is
     * <code>resolveProxyClass</code>.  For a given subclass of
     * <code>ObjectOutputStream</code> that overrides this method, the
     * <code>resolveProxyClass</code> method in the corresponding subclass of
     * <code>ObjectInputStream</code> must read any data or objects written by
     * <code>annotateProxyClass</code>.
     *
     * @param   cl the proxy class to annotate custom data for
     * @throws  IOException any exception thrown by the underlying
     *          <code>OutputStream</code>
     * @see ObjectInputStream#resolveProxyClass(String[])
     * @since   1.3
     */
    protected void annotateProxyClass(Class<?> cl) throws IOException {
    }

    
This method will allow trusted subclasses of ObjectOutputStream to
substitute one object for another during serialization. Replacing
objects is disabled until enableReplaceObject is called. The
enableReplaceObject method checks that the stream requesting to do
replacement can be trusted.  The first occurrence of each object written
into the serialization stream is passed to replaceObject.  Subsequent
references to the object are replaced by the object returned by the
original call to replaceObject.  To ensure that the private state of
objects is not unintentionally exposed, only trusted streams may use
replaceObject.
The ObjectOutputStream.writeObject method takes a parameter of type
Object (as opposed to type Serializable) to allow for cases where
non-serializable objects are replaced by serializable ones.
When a subclass is replacing objects it must insure that either a
complementary substitution must be made during deserialization or that
the substituted object is compatible with every field where the
reference will be stored.  Objects whose type is not a subclass of the
type of the field or array element abort the serialization by raising an
exception and the object is not be stored.
This method is called only once when each object is first
encountered.  All subsequent references to the object will be redirected
to the new object. This method should return the object to be
substituted or the original object.
Null can be returned as the object to be substituted, but may cause
NullReferenceException in classes that contain references to the
original object since they may be expecting an object instead of
null.
Params:
obj – the object to be replaced
Throws:
IOException – Any exception thrown by the underlying
         OutputStream.
Returns:
 the alternate object that replaced the specified one/**
     * This method will allow trusted subclasses of ObjectOutputStream to
     * substitute one object for another during serialization. Replacing
     * objects is disabled until enableReplaceObject is called. The
     * enableReplaceObject method checks that the stream requesting to do
     * replacement can be trusted.  The first occurrence of each object written
     * into the serialization stream is passed to replaceObject.  Subsequent
     * references to the object are replaced by the object returned by the
     * original call to replaceObject.  To ensure that the private state of
     * objects is not unintentionally exposed, only trusted streams may use
     * replaceObject.
     *
     * <p>The ObjectOutputStream.writeObject method takes a parameter of type
     * Object (as opposed to type Serializable) to allow for cases where
     * non-serializable objects are replaced by serializable ones.
     *
     * <p>When a subclass is replacing objects it must insure that either a
     * complementary substitution must be made during deserialization or that
     * the substituted object is compatible with every field where the
     * reference will be stored.  Objects whose type is not a subclass of the
     * type of the field or array element abort the serialization by raising an
     * exception and the object is not be stored.
     *
     * <p>This method is called only once when each object is first
     * encountered.  All subsequent references to the object will be redirected
     * to the new object. This method should return the object to be
     * substituted or the original object.
     *
     * <p>Null can be returned as the object to be substituted, but may cause
     * NullReferenceException in classes that contain references to the
     * original object since they may be expecting an object instead of
     * null.
     *
     * @param   obj the object to be replaced
     * @return  the alternate object that replaced the specified one
     * @throws  IOException Any exception thrown by the underlying
     *          OutputStream.
     */
    protected Object replaceObject(Object obj) throws IOException {
        return obj;
    }

    
Enables the stream to do replacement of objects written to the stream. When enabled, the replaceObject method is called for every object being serialized. 
If object replacement is currently not enabled, and enable is true, and there is a security manager installed, this method first calls the security manager's checkPermission method with the SerializablePermission("enableSubstitution") permission to ensure that the caller is permitted to enable the stream to do replacement of objects written to the stream. 
Params:
enable – true for enabling use of replaceObject for every object being serialized
Throws:
SecurityException – if a security manager exists and its checkPermission method denies enabling the stream to do replacement of objects written to the stream.
See Also:
SecurityManager.checkPermission
SerializablePermission
Returns:
 the previous setting before this method was invoked/**
     * Enables the stream to do replacement of objects written to the stream.  When
     * enabled, the {@link #replaceObject} method is called for every object being
     * serialized.
     *
     * <p>If object replacement is currently not enabled, and
     * {@code enable} is true, and there is a security manager installed,
     * this method first calls the security manager's
     * {@code checkPermission} method with the
     * {@code SerializablePermission("enableSubstitution")} permission to
     * ensure that the caller is permitted to enable the stream to do replacement
     * of objects written to the stream.
     *
     * @param   enable true for enabling use of {@code replaceObject} for
     *          every object being serialized
     * @return  the previous setting before this method was invoked
     * @throws  SecurityException if a security manager exists and its
     *          {@code checkPermission} method denies enabling the stream
     *          to do replacement of objects written to the stream.
     * @see SecurityManager#checkPermission
     * @see java.io.SerializablePermission
     */
    protected boolean enableReplaceObject(boolean enable)
        throws SecurityException
    {
        if (enable == enableReplace) {
            return enable;
        }
        if (enable) {
            SecurityManager sm = System.getSecurityManager();
            if (sm != null) {
                sm.checkPermission(SUBSTITUTION_PERMISSION);
            }
        }
        enableReplace = enable;
        return !enableReplace;
    }

    
The writeStreamHeader method is provided so subclasses can append or
prepend their own header to the stream.  It writes the magic number and
version to the stream.
Throws:
IOException – if I/O errors occur while writing to the underlying
         stream/**
     * The writeStreamHeader method is provided so subclasses can append or
     * prepend their own header to the stream.  It writes the magic number and
     * version to the stream.
     *
     * @throws  IOException if I/O errors occur while writing to the underlying
     *          stream
     */
    protected void writeStreamHeader() throws IOException {
        bout.writeShort(STREAM_MAGIC);
        bout.writeShort(STREAM_VERSION);
    }

    
Write the specified class descriptor to the ObjectOutputStream.  Class
descriptors are used to identify the classes of objects written to the
stream.  Subclasses of ObjectOutputStream may override this method to
customize the way in which class descriptors are written to the
serialization stream.  The corresponding method in ObjectInputStream,
readClassDescriptor, should then be overridden to
reconstitute the class descriptor from its custom stream representation.
By default, this method writes class descriptors according to the format
defined in the Object Serialization specification.
Note that this method will only be called if the ObjectOutputStream
is not using the old serialization stream format (set by calling
ObjectOutputStream's useProtocolVersion method).  If this
serialization stream is using the old format
(PROTOCOL_VERSION_1), the class descriptor will be written
internally in a manner that cannot be overridden or customized.
Params:
desc – class descriptor to write to the stream
Throws:
IOException – If an I/O error has occurred.
See Also:
ObjectInputStream.readClassDescriptor()
useProtocolVersion(int)
ObjectStreamConstants.PROTOCOL_VERSION_1
Since:
1.3/**
     * Write the specified class descriptor to the ObjectOutputStream.  Class
     * descriptors are used to identify the classes of objects written to the
     * stream.  Subclasses of ObjectOutputStream may override this method to
     * customize the way in which class descriptors are written to the
     * serialization stream.  The corresponding method in ObjectInputStream,
     * <code>readClassDescriptor</code>, should then be overridden to
     * reconstitute the class descriptor from its custom stream representation.
     * By default, this method writes class descriptors according to the format
     * defined in the Object Serialization specification.
     *
     * <p>Note that this method will only be called if the ObjectOutputStream
     * is not using the old serialization stream format (set by calling
     * ObjectOutputStream's <code>useProtocolVersion</code> method).  If this
     * serialization stream is using the old format
     * (<code>PROTOCOL_VERSION_1</code>), the class descriptor will be written
     * internally in a manner that cannot be overridden or customized.
     *
     * @param   desc class descriptor to write to the stream
     * @throws  IOException If an I/O error has occurred.
     * @see java.io.ObjectInputStream#readClassDescriptor()
     * @see #useProtocolVersion(int)
     * @see java.io.ObjectStreamConstants#PROTOCOL_VERSION_1
     * @since 1.3
     */
    protected void writeClassDescriptor(ObjectStreamClass desc)
        throws IOException
    {
        desc.writeNonProxy(this);
    }

    
Writes a byte. This method will block until the byte is actually
written.
Params:
val – the byte to be written to the stream
Throws:
IOException – If an I/O error has occurred./**
     * Writes a byte. This method will block until the byte is actually
     * written.
     *
     * @param   val the byte to be written to the stream
     * @throws  IOException If an I/O error has occurred.
     */
    public void write(int val) throws IOException {
        bout.write(val);
    }

    
Writes an array of bytes. This method will block until the bytes are
actually written.
Params:
buf – the data to be written
Throws:
IOException – If an I/O error has occurred./**
     * Writes an array of bytes. This method will block until the bytes are
     * actually written.
     *
     * @param   buf the data to be written
     * @throws  IOException If an I/O error has occurred.
     */
    public void write(byte[] buf) throws IOException {
        bout.write(buf, 0, buf.length, false);
    }

    
Writes a sub array of bytes.
Params:
buf – the data to be written
off – the start offset in the data
len – the number of bytes that are written
Throws:
IOException – If an I/O error has occurred./**
     * Writes a sub array of bytes.
     *
     * @param   buf the data to be written
     * @param   off the start offset in the data
     * @param   len the number of bytes that are written
     * @throws  IOException If an I/O error has occurred.
     */
    public void write(byte[] buf, int off, int len) throws IOException {
        if (buf == null) {
            throw new NullPointerException();
        }
        int endoff = off + len;
        if (off < 0 || len < 0 || endoff > buf.length || endoff < 0) {
            throw new IndexOutOfBoundsException();
        }
        bout.write(buf, off, len, false);
    }

    
Flushes the stream. This will write any buffered output bytes and flush
through to the underlying stream.
Throws:
IOException – If an I/O error has occurred./**
     * Flushes the stream. This will write any buffered output bytes and flush
     * through to the underlying stream.
     *
     * @throws  IOException If an I/O error has occurred.
     */
    public void flush() throws IOException {
        bout.flush();
    }

    
Drain any buffered data in ObjectOutputStream.  Similar to flush but
does not propagate the flush to the underlying stream.
Throws:
IOException – if I/O errors occur while writing to the underlying
         stream/**
     * Drain any buffered data in ObjectOutputStream.  Similar to flush but
     * does not propagate the flush to the underlying stream.
     *
     * @throws  IOException if I/O errors occur while writing to the underlying
     *          stream
     */
    protected void drain() throws IOException {
        bout.drain();
    }

    
Closes the stream. This method must be called to release any resources
associated with the stream.
Throws:
IOException – If an I/O error has occurred./**
     * Closes the stream. This method must be called to release any resources
     * associated with the stream.
     *
     * @throws  IOException If an I/O error has occurred.
     */
    public void close() throws IOException {
        flush();
        clear();
        bout.close();
    }

    
Writes a boolean.
Params:
val – the boolean to be written
Throws:
IOException – if I/O errors occur while writing to the underlying
         stream/**
     * Writes a boolean.
     *
     * @param   val the boolean to be written
     * @throws  IOException if I/O errors occur while writing to the underlying
     *          stream
     */
    public void writeBoolean(boolean val) throws IOException {
        bout.writeBoolean(val);
    }

    
Writes an 8 bit byte.
Params:
val – the byte value to be written
Throws:
IOException – if I/O errors occur while writing to the underlying
         stream/**
     * Writes an 8 bit byte.
     *
     * @param   val the byte value to be written
     * @throws  IOException if I/O errors occur while writing to the underlying
     *          stream
     */
    public void writeByte(int val) throws IOException  {
        bout.writeByte(val);
    }

    
Writes a 16 bit short.
Params:
val – the short value to be written
Throws:
IOException – if I/O errors occur while writing to the underlying
         stream/**
     * Writes a 16 bit short.
     *
     * @param   val the short value to be written
     * @throws  IOException if I/O errors occur while writing to the underlying
     *          stream
     */
    public void writeShort(int val)  throws IOException {
        bout.writeShort(val);
    }

    
Writes a 16 bit char.
Params:
val – the char value to be written
Throws:
IOException – if I/O errors occur while writing to the underlying
         stream/**
     * Writes a 16 bit char.
     *
     * @param   val the char value to be written
     * @throws  IOException if I/O errors occur while writing to the underlying
     *          stream
     */
    public void writeChar(int val)  throws IOException {
        bout.writeChar(val);
    }

    
Writes a 32 bit int.
Params:
val – the integer value to be written
Throws:
IOException – if I/O errors occur while writing to the underlying
         stream/**
     * Writes a 32 bit int.
     *
     * @param   val the integer value to be written
     * @throws  IOException if I/O errors occur while writing to the underlying
     *          stream
     */
    public void writeInt(int val)  throws IOException {
        bout.writeInt(val);
    }

    
Writes a 64 bit long.
Params:
val – the long value to be written
Throws:
IOException – if I/O errors occur while writing to the underlying
         stream/**
     * Writes a 64 bit long.
     *
     * @param   val the long value to be written
     * @throws  IOException if I/O errors occur while writing to the underlying
     *          stream
     */
    public void writeLong(long val)  throws IOException {
        bout.writeLong(val);
    }

    
Writes a 32 bit float.
Params:
val – the float value to be written
Throws:
IOException – if I/O errors occur while writing to the underlying
         stream/**
     * Writes a 32 bit float.
     *
     * @param   val the float value to be written
     * @throws  IOException if I/O errors occur while writing to the underlying
     *          stream
     */
    public void writeFloat(float val) throws IOException {
        bout.writeFloat(val);
    }

    
Writes a 64 bit double.
Params:
val – the double value to be written
Throws:
IOException – if I/O errors occur while writing to the underlying
         stream/**
     * Writes a 64 bit double.
     *
     * @param   val the double value to be written
     * @throws  IOException if I/O errors occur while writing to the underlying
     *          stream
     */
    public void writeDouble(double val) throws IOException {
        bout.writeDouble(val);
    }

    
Writes a String as a sequence of bytes.
Params:
str – the String of bytes to be written
Throws:
IOException – if I/O errors occur while writing to the underlying
         stream/**
     * Writes a String as a sequence of bytes.
     *
     * @param   str the String of bytes to be written
     * @throws  IOException if I/O errors occur while writing to the underlying
     *          stream
     */
    public void writeBytes(String str) throws IOException {
        bout.writeBytes(str);
    }

    
Writes a String as a sequence of chars.
Params:
str – the String of chars to be written
Throws:
IOException – if I/O errors occur while writing to the underlying
         stream/**
     * Writes a String as a sequence of chars.
     *
     * @param   str the String of chars to be written
     * @throws  IOException if I/O errors occur while writing to the underlying
     *          stream
     */
    public void writeChars(String str) throws IOException {
        bout.writeChars(str);
    }

    
Primitive data write of this String in
modified UTF-8
format.  Note that there is a
significant difference between writing a String into the stream as
primitive data or as an Object. A String instance written by writeObject
is written into the stream as a String initially. Future writeObject()
calls write references to the string into the stream.
Params:
str – the String to be written
Throws:
IOException – if I/O errors occur while writing to the underlying
         stream/**
     * Primitive data write of this String in
     * <a href="DataInput.html#modified-utf-8">modified UTF-8</a>
     * format.  Note that there is a
     * significant difference between writing a String into the stream as
     * primitive data or as an Object. A String instance written by writeObject
     * is written into the stream as a String initially. Future writeObject()
     * calls write references to the string into the stream.
     *
     * @param   str the String to be written
     * @throws  IOException if I/O errors occur while writing to the underlying
     *          stream
     */
    public void writeUTF(String str) throws IOException {
        bout.writeUTF(str);
    }

    
Provide programmatic access to the persistent fields to be written
to ObjectOutput.
Since:
1.2/**
     * Provide programmatic access to the persistent fields to be written
     * to ObjectOutput.
     *
     * @since 1.2
     */
    public abstract static class PutField {

        
Put the value of the named boolean field into the persistent field.
Params:
name – the name of the serializable field
val – the value to assign to the field
Throws:
IllegalArgumentException – if name does not
match the name of a serializable field for the class whose fields
are being written, or if the type of the named field is not
boolean/**
         * Put the value of the named boolean field into the persistent field.
         *
         * @param  name the name of the serializable field
         * @param  val the value to assign to the field
         * @throws IllegalArgumentException if <code>name</code> does not
         * match the name of a serializable field for the class whose fields
         * are being written, or if the type of the named field is not
         * <code>boolean</code>
         */
        public abstract void put(String name, boolean val);

        
Put the value of the named byte field into the persistent field.
Params:
name – the name of the serializable field
val – the value to assign to the field
Throws:
IllegalArgumentException – if name does not
match the name of a serializable field for the class whose fields
are being written, or if the type of the named field is not
byte/**
         * Put the value of the named byte field into the persistent field.
         *
         * @param  name the name of the serializable field
         * @param  val the value to assign to the field
         * @throws IllegalArgumentException if <code>name</code> does not
         * match the name of a serializable field for the class whose fields
         * are being written, or if the type of the named field is not
         * <code>byte</code>
         */
        public abstract void put(String name, byte val);

        
Put the value of the named char field into the persistent field.
Params:
name – the name of the serializable field
val – the value to assign to the field
Throws:
IllegalArgumentException – if name does not
match the name of a serializable field for the class whose fields
are being written, or if the type of the named field is not
char/**
         * Put the value of the named char field into the persistent field.
         *
         * @param  name the name of the serializable field
         * @param  val the value to assign to the field
         * @throws IllegalArgumentException if <code>name</code> does not
         * match the name of a serializable field for the class whose fields
         * are being written, or if the type of the named field is not
         * <code>char</code>
         */
        public abstract void put(String name, char val);

        
Put the value of the named short field into the persistent field.
Params:
name – the name of the serializable field
val – the value to assign to the field
Throws:
IllegalArgumentException – if name does not
match the name of a serializable field for the class whose fields
are being written, or if the type of the named field is not
short/**
         * Put the value of the named short field into the persistent field.
         *
         * @param  name the name of the serializable field
         * @param  val the value to assign to the field
         * @throws IllegalArgumentException if <code>name</code> does not
         * match the name of a serializable field for the class whose fields
         * are being written, or if the type of the named field is not
         * <code>short</code>
         */
        public abstract void put(String name, short val);

        
Put the value of the named int field into the persistent field.
Params:
name – the name of the serializable field
val – the value to assign to the field
Throws:
IllegalArgumentException – if name does not
match the name of a serializable field for the class whose fields
are being written, or if the type of the named field is not
int/**
         * Put the value of the named int field into the persistent field.
         *
         * @param  name the name of the serializable field
         * @param  val the value to assign to the field
         * @throws IllegalArgumentException if <code>name</code> does not
         * match the name of a serializable field for the class whose fields
         * are being written, or if the type of the named field is not
         * <code>int</code>
         */
        public abstract void put(String name, int val);

        
Put the value of the named long field into the persistent field.
Params:
name – the name of the serializable field
val – the value to assign to the field
Throws:
IllegalArgumentException – if name does not
match the name of a serializable field for the class whose fields
are being written, or if the type of the named field is not
long/**
         * Put the value of the named long field into the persistent field.
         *
         * @param  name the name of the serializable field
         * @param  val the value to assign to the field
         * @throws IllegalArgumentException if <code>name</code> does not
         * match the name of a serializable field for the class whose fields
         * are being written, or if the type of the named field is not
         * <code>long</code>
         */
        public abstract void put(String name, long val);

        
Put the value of the named float field into the persistent field.
Params:
name – the name of the serializable field
val – the value to assign to the field
Throws:
IllegalArgumentException – if name does not
match the name of a serializable field for the class whose fields
are being written, or if the type of the named field is not
float/**
         * Put the value of the named float field into the persistent field.
         *
         * @param  name the name of the serializable field
         * @param  val the value to assign to the field
         * @throws IllegalArgumentException if <code>name</code> does not
         * match the name of a serializable field for the class whose fields
         * are being written, or if the type of the named field is not
         * <code>float</code>
         */
        public abstract void put(String name, float val);

        
Put the value of the named double field into the persistent field.
Params:
name – the name of the serializable field
val – the value to assign to the field
Throws:
IllegalArgumentException – if name does not
match the name of a serializable field for the class whose fields
are being written, or if the type of the named field is not
double/**
         * Put the value of the named double field into the persistent field.
         *
         * @param  name the name of the serializable field
         * @param  val the value to assign to the field
         * @throws IllegalArgumentException if <code>name</code> does not
         * match the name of a serializable field for the class whose fields
         * are being written, or if the type of the named field is not
         * <code>double</code>
         */
        public abstract void put(String name, double val);

        
Put the value of the named Object field into the persistent field.
Params:
name – the name of the serializable field
val – the value to assign to the field
        (which may be null)
Throws:
IllegalArgumentException – if name does not
match the name of a serializable field for the class whose fields
are being written, or if the type of the named field is not a
reference type/**
         * Put the value of the named Object field into the persistent field.
         *
         * @param  name the name of the serializable field
         * @param  val the value to assign to the field
         *         (which may be <code>null</code>)
         * @throws IllegalArgumentException if <code>name</code> does not
         * match the name of a serializable field for the class whose fields
         * are being written, or if the type of the named field is not a
         * reference type
         */
        public abstract void put(String name, Object val);

        
Write the data and fields to the specified ObjectOutput stream,
which must be the same stream that produced this
PutField object.
Params:
out – the stream to write the data and fields to
Throws:
IOException – if I/O errors occur while writing to the
        underlying stream
IllegalArgumentException – if the specified stream is not
        the same stream that produced this PutField
        object
Deprecated:
This method does not write the values contained by this
        PutField object in a proper format, and may
        result in corruption of the serialization stream.  The
        correct way to write PutField data is by calling the ObjectOutputStream.writeFields() method./**
         * Write the data and fields to the specified ObjectOutput stream,
         * which must be the same stream that produced this
         * <code>PutField</code> object.
         *
         * @param  out the stream to write the data and fields to
         * @throws IOException if I/O errors occur while writing to the
         *         underlying stream
         * @throws IllegalArgumentException if the specified stream is not
         *         the same stream that produced this <code>PutField</code>
         *         object
         * @deprecated This method does not write the values contained by this
         *         <code>PutField</code> object in a proper format, and may
         *         result in corruption of the serialization stream.  The
         *         correct way to write <code>PutField</code> data is by
         *         calling the {@link java.io.ObjectOutputStream#writeFields()}
         *         method.
         */
        @Deprecated
        public abstract void write(ObjectOutput out) throws IOException;
    }


    
Returns protocol version in use.
/**
     * Returns protocol version in use.
     */
    int getProtocolVersion() {
        return protocol;
    }

    
Writes string without allowing it to be replaced in stream.  Used by
ObjectStreamClass to write class descriptor type strings.
/**
     * Writes string without allowing it to be replaced in stream.  Used by
     * ObjectStreamClass to write class descriptor type strings.
     */
    void writeTypeString(String str) throws IOException {
        int handle;
        if (str == null) {
            writeNull();
        } else if ((handle = handles.lookup(str)) != -1) {
            writeHandle(handle);
        } else {
            writeString(str, false);
        }
    }

    
Verifies that this (possibly subclass) instance can be constructed
without violating security constraints: the subclass must not override
security-sensitive non-final methods, or else the
"enableSubclassImplementation" SerializablePermission is checked.
/**
     * Verifies that this (possibly subclass) instance can be constructed
     * without violating security constraints: the subclass must not override
     * security-sensitive non-final methods, or else the
     * "enableSubclassImplementation" SerializablePermission is checked.
     */
    private void verifySubclass() {
        Class<?> cl = getClass();
        if (cl == ObjectOutputStream.class) {
            return;
        }
        SecurityManager sm = System.getSecurityManager();
        if (sm == null) {
            return;
        }
        processQueue(Caches.subclassAuditsQueue, Caches.subclassAudits);
        WeakClassKey key = new WeakClassKey(cl, Caches.subclassAuditsQueue);
        Boolean result = Caches.subclassAudits.get(key);
        if (result == null) {
            result = auditSubclass(cl);
            Caches.subclassAudits.putIfAbsent(key, result);
        }
        if (!result) {
            sm.checkPermission(SUBCLASS_IMPLEMENTATION_PERMISSION);
        }
    }

    
Performs reflective checks on given subclass to verify that it doesn't
override security-sensitive non-final methods.  Returns TRUE if subclass
is "safe", FALSE otherwise.
/**
     * Performs reflective checks on given subclass to verify that it doesn't
     * override security-sensitive non-final methods.  Returns TRUE if subclass
     * is "safe", FALSE otherwise.
     */
    private static Boolean auditSubclass(Class<?> subcl) {
        return AccessController.doPrivileged(
            new PrivilegedAction<>() {
                public Boolean run() {
                    for (Class<?> cl = subcl;
                         cl != ObjectOutputStream.class;
                         cl = cl.getSuperclass())
                    {
                        try {
                            cl.getDeclaredMethod(
                                "writeUnshared", new Class<?>[] { Object.class });
                            return Boolean.FALSE;
                        } catch (NoSuchMethodException ex) {
                        }
                        try {
                            cl.getDeclaredMethod("putFields", (Class<?>[]) null);
                            return Boolean.FALSE;
                        } catch (NoSuchMethodException ex) {
                        }
                    }
                    return Boolean.TRUE;
                }
            }
        );
    }

    
Clears internal data structures.
/**
     * Clears internal data structures.
     */
    private void clear() {
        subs.clear();
        handles.clear();
    }

    
Underlying writeObject/writeUnshared implementation.
/**
     * Underlying writeObject/writeUnshared implementation.
     */
    private void writeObject0(Object obj, boolean unshared)
        throws IOException
    {
        boolean oldMode = bout.setBlockDataMode(false);
        depth++;
        try {
            // handle previously written and non-replaceable objects
            int h;
            if ((obj = subs.lookup(obj)) == null) {
                writeNull();
                return;
            } else if (!unshared && (h = handles.lookup(obj)) != -1) {
                writeHandle(h);
                return;
            } else if (obj instanceof Class) {
                writeClass((Class) obj, unshared);
                return;
            } else if (obj instanceof ObjectStreamClass) {
                writeClassDesc((ObjectStreamClass) obj, unshared);
                return;
            }

            // check for replacement object
            Object orig = obj;
            Class<?> cl = obj.getClass();
            ObjectStreamClass desc;
            for (;;) {
                // REMIND: skip this check for strings/arrays?
                Class<?> repCl;
                desc = ObjectStreamClass.lookup(cl, true);
                if (!desc.hasWriteReplaceMethod() ||
                    (obj = desc.invokeWriteReplace(obj)) == null ||
                    (repCl = obj.getClass()) == cl)
                {
                    break;
                }
                cl = repCl;
            }
            if (enableReplace) {
                Object rep = replaceObject(obj);
                if (rep != obj && rep != null) {
                    cl = rep.getClass();
                    desc = ObjectStreamClass.lookup(cl, true);
                }
                obj = rep;
            }

            // if object replaced, run through original checks a second time
            if (obj != orig) {
                subs.assign(orig, obj);
                if (obj == null) {
                    writeNull();
                    return;
                } else if (!unshared && (h = handles.lookup(obj)) != -1) {
                    writeHandle(h);
                    return;
                } else if (obj instanceof Class) {
                    writeClass((Class) obj, unshared);
                    return;
                } else if (obj instanceof ObjectStreamClass) {
                    writeClassDesc((ObjectStreamClass) obj, unshared);
                    return;
                }
            }

            // remaining cases
            if (obj instanceof String) {
                writeString((String) obj, unshared);
            } else if (cl.isArray()) {
                writeArray(obj, desc, unshared);
            } else if (obj instanceof Enum) {
                writeEnum((Enum<?>) obj, desc, unshared);
            } else if (obj instanceof Serializable) {
                writeOrdinaryObject(obj, desc, unshared);
            } else {
                if (extendedDebugInfo) {
                    throw new NotSerializableException(
                        cl.getName() + "\n" + debugInfoStack.toString());
                } else {
                    throw new NotSerializableException(cl.getName());
                }
            }
        } finally {
            depth--;
            bout.setBlockDataMode(oldMode);
        }
    }

    
Writes null code to stream.
/**
     * Writes null code to stream.
     */
    private void writeNull() throws IOException {
        bout.writeByte(TC_NULL);
    }

    
Writes given object handle to stream.
/**
     * Writes given object handle to stream.
     */
    private void writeHandle(int handle) throws IOException {
        bout.writeByte(TC_REFERENCE);
        bout.writeInt(baseWireHandle + handle);
    }

    
Writes representation of given class to stream.
/**
     * Writes representation of given class to stream.
     */
    private void writeClass(Class<?> cl, boolean unshared) throws IOException {
        bout.writeByte(TC_CLASS);
        writeClassDesc(ObjectStreamClass.lookup(cl, true), false);
        handles.assign(unshared ? null : cl);
    }

    
Writes representation of given class descriptor to stream.
/**
     * Writes representation of given class descriptor to stream.
     */
    private void writeClassDesc(ObjectStreamClass desc, boolean unshared)
        throws IOException
    {
        int handle;
        if (desc == null) {
            writeNull();
        } else if (!unshared && (handle = handles.lookup(desc)) != -1) {
            writeHandle(handle);
        } else if (desc.isProxy()) {
            writeProxyDesc(desc, unshared);
        } else {
            writeNonProxyDesc(desc, unshared);
        }
    }

    private boolean isCustomSubclass() {
        // Return true if this class is a custom subclass of ObjectOutputStream
        return getClass().getClassLoader()
                   != ObjectOutputStream.class.getClassLoader();
    }

    
Writes class descriptor representing a dynamic proxy class to stream.
/**
     * Writes class descriptor representing a dynamic proxy class to stream.
     */
    private void writeProxyDesc(ObjectStreamClass desc, boolean unshared)
        throws IOException
    {
        bout.writeByte(TC_PROXYCLASSDESC);
        handles.assign(unshared ? null : desc);

        Class<?> cl = desc.forClass();
        Class<?>[] ifaces = cl.getInterfaces();
        bout.writeInt(ifaces.length);
        for (int i = 0; i < ifaces.length; i++) {
            bout.writeUTF(ifaces[i].getName());
        }

        bout.setBlockDataMode(true);
        if (cl != null && isCustomSubclass()) {
            ReflectUtil.checkPackageAccess(cl);
        }
        annotateProxyClass(cl);
        bout.setBlockDataMode(false);
        bout.writeByte(TC_ENDBLOCKDATA);

        writeClassDesc(desc.getSuperDesc(), false);
    }

    
Writes class descriptor representing a standard (i.e., not a dynamic
proxy) class to stream.
/**
     * Writes class descriptor representing a standard (i.e., not a dynamic
     * proxy) class to stream.
     */
    private void writeNonProxyDesc(ObjectStreamClass desc, boolean unshared)
        throws IOException
    {
        bout.writeByte(TC_CLASSDESC);
        handles.assign(unshared ? null : desc);

        if (protocol == PROTOCOL_VERSION_1) {
            // do not invoke class descriptor write hook with old protocol
            desc.writeNonProxy(this);
        } else {
            writeClassDescriptor(desc);
        }

        Class<?> cl = desc.forClass();
        bout.setBlockDataMode(true);
        if (cl != null && isCustomSubclass()) {
            ReflectUtil.checkPackageAccess(cl);
        }
        annotateClass(cl);
        bout.setBlockDataMode(false);
        bout.writeByte(TC_ENDBLOCKDATA);

        writeClassDesc(desc.getSuperDesc(), false);
    }

    
Writes given string to stream, using standard or long UTF format
depending on string length.
/**
     * Writes given string to stream, using standard or long UTF format
     * depending on string length.
     */
    private void writeString(String str, boolean unshared) throws IOException {
        handles.assign(unshared ? null : str);
        long utflen = bout.getUTFLength(str);
        if (utflen <= 0xFFFF) {
            bout.writeByte(TC_STRING);
            bout.writeUTF(str, utflen);
        } else {
            bout.writeByte(TC_LONGSTRING);
            bout.writeLongUTF(str, utflen);
        }
    }

    
Writes given array object to stream.
/**
     * Writes given array object to stream.
     */
    private void writeArray(Object array,
                            ObjectStreamClass desc,
                            boolean unshared)
        throws IOException
    {
        bout.writeByte(TC_ARRAY);
        writeClassDesc(desc, false);
        handles.assign(unshared ? null : array);

        Class<?> ccl = desc.forClass().getComponentType();
        if (ccl.isPrimitive()) {
            if (ccl == Integer.TYPE) {
                int[] ia = (int[]) array;
                bout.writeInt(ia.length);
                bout.writeInts(ia, 0, ia.length);
            } else if (ccl == Byte.TYPE) {
                byte[] ba = (byte[]) array;
                bout.writeInt(ba.length);
                bout.write(ba, 0, ba.length, true);
            } else if (ccl == Long.TYPE) {
                long[] ja = (long[]) array;
                bout.writeInt(ja.length);
                bout.writeLongs(ja, 0, ja.length);
            } else if (ccl == Float.TYPE) {
                float[] fa = (float[]) array;
                bout.writeInt(fa.length);
                bout.writeFloats(fa, 0, fa.length);
            } else if (ccl == Double.TYPE) {
                double[] da = (double[]) array;
                bout.writeInt(da.length);
                bout.writeDoubles(da, 0, da.length);
            } else if (ccl == Short.TYPE) {
                short[] sa = (short[]) array;
                bout.writeInt(sa.length);
                bout.writeShorts(sa, 0, sa.length);
            } else if (ccl == Character.TYPE) {
                char[] ca = (char[]) array;
                bout.writeInt(ca.length);
                bout.writeChars(ca, 0, ca.length);
            } else if (ccl == Boolean.TYPE) {
                boolean[] za = (boolean[]) array;
                bout.writeInt(za.length);
                bout.writeBooleans(za, 0, za.length);
            } else {
                throw new InternalError();
            }
        } else {
            Object[] objs = (Object[]) array;
            int len = objs.length;
            bout.writeInt(len);
            if (extendedDebugInfo) {
                debugInfoStack.push(
                    "array (class \"" + array.getClass().getName() +
                    "\", size: " + len  + ")");
            }
            try {
                for (int i = 0; i < len; i++) {
                    if (extendedDebugInfo) {
                        debugInfoStack.push(
                            "element of array (index: " + i + ")");
                    }
                    try {
                        writeObject0(objs[i], false);
                    } finally {
                        if (extendedDebugInfo) {
                            debugInfoStack.pop();
                        }
                    }
                }
            } finally {
                if (extendedDebugInfo) {
                    debugInfoStack.pop();
                }
            }
        }
    }

    
Writes given enum constant to stream.
/**
     * Writes given enum constant to stream.
     */
    private void writeEnum(Enum<?> en,
                           ObjectStreamClass desc,
                           boolean unshared)
        throws IOException
    {
        bout.writeByte(TC_ENUM);
        ObjectStreamClass sdesc = desc.getSuperDesc();
        writeClassDesc((sdesc.forClass() == Enum.class) ? desc : sdesc, false);
        handles.assign(unshared ? null : en);
        writeString(en.name(), false);
    }

    
Writes representation of a "ordinary" (i.e., not a String, Class,
ObjectStreamClass, array, or enum constant) serializable object to the
stream.
/**
     * Writes representation of a "ordinary" (i.e., not a String, Class,
     * ObjectStreamClass, array, or enum constant) serializable object to the
     * stream.
     */
    private void writeOrdinaryObject(Object obj,
                                     ObjectStreamClass desc,
                                     boolean unshared)
        throws IOException
    {
        if (extendedDebugInfo) {
            debugInfoStack.push(
                (depth == 1 ? "root " : "") + "object (class \"" +
                obj.getClass().getName() + "\", " + obj.toString() + ")");
        }
        try {
            desc.checkSerialize();

            bout.writeByte(TC_OBJECT);
            writeClassDesc(desc, false);
            handles.assign(unshared ? null : obj);
            if (desc.isExternalizable() && !desc.isProxy()) {
                writeExternalData((Externalizable) obj);
            } else {
                writeSerialData(obj, desc);
            }
        } finally {
            if (extendedDebugInfo) {
                debugInfoStack.pop();
            }
        }
    }

    
Writes externalizable data of given object by invoking its
writeExternal() method.
/**
     * Writes externalizable data of given object by invoking its
     * writeExternal() method.
     */
    private void writeExternalData(Externalizable obj) throws IOException {
        PutFieldImpl oldPut = curPut;
        curPut = null;

        if (extendedDebugInfo) {
            debugInfoStack.push("writeExternal data");
        }
        SerialCallbackContext oldContext = curContext;
        try {
            curContext = null;
            if (protocol == PROTOCOL_VERSION_1) {
                obj.writeExternal(this);
            } else {
                bout.setBlockDataMode(true);
                obj.writeExternal(this);
                bout.setBlockDataMode(false);
                bout.writeByte(TC_ENDBLOCKDATA);
            }
        } finally {
            curContext = oldContext;
            if (extendedDebugInfo) {
                debugInfoStack.pop();
            }
        }

        curPut = oldPut;
    }

    
Writes instance data for each serializable class of given object, from
superclass to subclass.
/**
     * Writes instance data for each serializable class of given object, from
     * superclass to subclass.
     */
    private void writeSerialData(Object obj, ObjectStreamClass desc)
        throws IOException
    {
        ObjectStreamClass.ClassDataSlot[] slots = desc.getClassDataLayout();
        for (int i = 0; i < slots.length; i++) {
            ObjectStreamClass slotDesc = slots[i].desc;
            if (slotDesc.hasWriteObjectMethod()) {
                PutFieldImpl oldPut = curPut;
                curPut = null;
                SerialCallbackContext oldContext = curContext;

                if (extendedDebugInfo) {
                    debugInfoStack.push(
                        "custom writeObject data (class \"" +
                        slotDesc.getName() + "\")");
                }
                try {
                    curContext = new SerialCallbackContext(obj, slotDesc);
                    bout.setBlockDataMode(true);
                    slotDesc.invokeWriteObject(obj, this);
                    bout.setBlockDataMode(false);
                    bout.writeByte(TC_ENDBLOCKDATA);
                } finally {
                    curContext.setUsed();
                    curContext = oldContext;
                    if (extendedDebugInfo) {
                        debugInfoStack.pop();
                    }
                }

                curPut = oldPut;
            } else {
                defaultWriteFields(obj, slotDesc);
            }
        }
    }

    
Fetches and writes values of serializable fields of given object to
stream.  The given class descriptor specifies which field values to
write, and in which order they should be written.
/**
     * Fetches and writes values of serializable fields of given object to
     * stream.  The given class descriptor specifies which field values to
     * write, and in which order they should be written.
     */
    private void defaultWriteFields(Object obj, ObjectStreamClass desc)
        throws IOException
    {
        Class<?> cl = desc.forClass();
        if (cl != null && obj != null && !cl.isInstance(obj)) {
            throw new ClassCastException();
        }

        desc.checkDefaultSerialize();

        int primDataSize = desc.getPrimDataSize();
        if (primDataSize > 0) {
            if (primVals == null || primVals.length < primDataSize) {
                primVals = new byte[primDataSize];
            }
            desc.getPrimFieldValues(obj, primVals);
            bout.write(primVals, 0, primDataSize, false);
        }

        int numObjFields = desc.getNumObjFields();
        if (numObjFields > 0) {
            ObjectStreamField[] fields = desc.getFields(false);
            Object[] objVals = new Object[numObjFields];
            int numPrimFields = fields.length - objVals.length;
            desc.getObjFieldValues(obj, objVals);
            for (int i = 0; i < objVals.length; i++) {
                if (extendedDebugInfo) {
                    debugInfoStack.push(
                        "field (class \"" + desc.getName() + "\", name: \"" +
                        fields[numPrimFields + i].getName() + "\", type: \"" +
                        fields[numPrimFields + i].getType() + "\")");
                }
                try {
                    writeObject0(objVals[i],
                                 fields[numPrimFields + i].isUnshared());
                } finally {
                    if (extendedDebugInfo) {
                        debugInfoStack.pop();
                    }
                }
            }
        }
    }

    
Attempts to write to stream fatal IOException that has caused
serialization to abort.
/**
     * Attempts to write to stream fatal IOException that has caused
     * serialization to abort.
     */
    private void writeFatalException(IOException ex) throws IOException {
        /*
         * Note: the serialization specification states that if a second
         * IOException occurs while attempting to serialize the original fatal
         * exception to the stream, then a StreamCorruptedException should be
         * thrown (section 2.1).  However, due to a bug in previous
         * implementations of serialization, StreamCorruptedExceptions were
         * rarely (if ever) actually thrown--the "root" exceptions from
         * underlying streams were thrown instead.  This historical behavior is
         * followed here for consistency.
         */
        clear();
        boolean oldMode = bout.setBlockDataMode(false);
        try {
            bout.writeByte(TC_EXCEPTION);
            writeObject0(ex, false);
            clear();
        } finally {
            bout.setBlockDataMode(oldMode);
        }
    }

    
Converts specified span of float values into byte values.
/**
     * Converts specified span of float values into byte values.
     */
    // REMIND: remove once hotspot inlines Float.floatToIntBits
    private static native void floatsToBytes(float[] src, int srcpos,
                                             byte[] dst, int dstpos,
                                             int nfloats);

    
Converts specified span of double values into byte values.
/**
     * Converts specified span of double values into byte values.
     */
    // REMIND: remove once hotspot inlines Double.doubleToLongBits
    private static native void doublesToBytes(double[] src, int srcpos,
                                              byte[] dst, int dstpos,
                                              int ndoubles);

    
Default PutField implementation.
/**
     * Default PutField implementation.
     */
    private class PutFieldImpl extends PutField {

        
class descriptor describing serializable fields /** class descriptor describing serializable fields */
        private final ObjectStreamClass desc;
        
primitive field values /** primitive field values */
        private final byte[] primVals;
        
object field values /** object field values */
        private final Object[] objVals;

        
Creates PutFieldImpl object for writing fields defined in given
class descriptor.
/**
         * Creates PutFieldImpl object for writing fields defined in given
         * class descriptor.
         */
        PutFieldImpl(ObjectStreamClass desc) {
            this.desc = desc;
            primVals = new byte[desc.getPrimDataSize()];
            objVals = new Object[desc.getNumObjFields()];
        }

        public void put(String name, boolean val) {
            Bits.putBoolean(primVals, getFieldOffset(name, Boolean.TYPE), val);
        }

        public void put(String name, byte val) {
            primVals[getFieldOffset(name, Byte.TYPE)] = val;
        }

        public void put(String name, char val) {
            Bits.putChar(primVals, getFieldOffset(name, Character.TYPE), val);
        }

        public void put(String name, short val) {
            Bits.putShort(primVals, getFieldOffset(name, Short.TYPE), val);
        }

        public void put(String name, int val) {
            Bits.putInt(primVals, getFieldOffset(name, Integer.TYPE), val);
        }

        public void put(String name, float val) {
            Bits.putFloat(primVals, getFieldOffset(name, Float.TYPE), val);
        }

        public void put(String name, long val) {
            Bits.putLong(primVals, getFieldOffset(name, Long.TYPE), val);
        }

        public void put(String name, double val) {
            Bits.putDouble(primVals, getFieldOffset(name, Double.TYPE), val);
        }

        public void put(String name, Object val) {
            objVals[getFieldOffset(name, Object.class)] = val;
        }

        // deprecated in ObjectOutputStream.PutField
        public void write(ObjectOutput out) throws IOException {
            /*
             * Applications should *not* use this method to write PutField
             * data, as it will lead to stream corruption if the PutField
             * object writes any primitive data (since block data mode is not
             * unset/set properly, as is done in OOS.writeFields()).  This
             * broken implementation is being retained solely for behavioral
             * compatibility, in order to support applications which use
             * OOS.PutField.write() for writing only non-primitive data.
             *
             * Serialization of unshared objects is not implemented here since
             * it is not necessary for backwards compatibility; also, unshared
             * semantics may not be supported by the given ObjectOutput
             * instance.  Applications which write unshared objects using the
             * PutField API must use OOS.writeFields().
             */
            if (ObjectOutputStream.this != out) {
                throw new IllegalArgumentException("wrong stream");
            }
            out.write(primVals, 0, primVals.length);

            ObjectStreamField[] fields = desc.getFields(false);
            int numPrimFields = fields.length - objVals.length;
            // REMIND: warn if numPrimFields > 0?
            for (int i = 0; i < objVals.length; i++) {
                if (fields[numPrimFields + i].isUnshared()) {
                    throw new IOException("cannot write unshared object");
                }
                out.writeObject(objVals[i]);
            }
        }

        
Writes buffered primitive data and object fields to stream.
/**
         * Writes buffered primitive data and object fields to stream.
         */
        void writeFields() throws IOException {
            bout.write(primVals, 0, primVals.length, false);

            ObjectStreamField[] fields = desc.getFields(false);
            int numPrimFields = fields.length - objVals.length;
            for (int i = 0; i < objVals.length; i++) {
                if (extendedDebugInfo) {
                    debugInfoStack.push(
                        "field (class \"" + desc.getName() + "\", name: \"" +
                        fields[numPrimFields + i].getName() + "\", type: \"" +
                        fields[numPrimFields + i].getType() + "\")");
                }
                try {
                    writeObject0(objVals[i],
                                 fields[numPrimFields + i].isUnshared());
                } finally {
                    if (extendedDebugInfo) {
                        debugInfoStack.pop();
                    }
                }
            }
        }

        
Returns offset of field with given name and type.  A specified type
of null matches all types, Object.class matches all non-primitive
types, and any other non-null type matches assignable types only.
Throws IllegalArgumentException if no matching field found.
/**
         * Returns offset of field with given name and type.  A specified type
         * of null matches all types, Object.class matches all non-primitive
         * types, and any other non-null type matches assignable types only.
         * Throws IllegalArgumentException if no matching field found.
         */
        private int getFieldOffset(String name, Class<?> type) {
            ObjectStreamField field = desc.getField(name, type);
            if (field == null) {
                throw new IllegalArgumentException("no such field " + name +
                                                   " with type " + type);
            }
            return field.getOffset();
        }
    }

    
Buffered output stream with two modes: in default mode, outputs data in
same format as DataOutputStream; in "block data" mode, outputs data
bracketed by block data markers (see object serialization specification
for details).
/**
     * Buffered output stream with two modes: in default mode, outputs data in
     * same format as DataOutputStream; in "block data" mode, outputs data
     * bracketed by block data markers (see object serialization specification
     * for details).
     */
    private static class BlockDataOutputStream
        extends OutputStream implements DataOutput
    {
        
maximum data block length /** maximum data block length */
        private static final int MAX_BLOCK_SIZE = 1024;
        
maximum data block header length /** maximum data block header length */
        private static final int MAX_HEADER_SIZE = 5;
        
(tunable) length of char buffer (for writing strings) /** (tunable) length of char buffer (for writing strings) */
        private static final int CHAR_BUF_SIZE = 256;

        
buffer for writing general/block data /** buffer for writing general/block data */
        private final byte[] buf = new byte[MAX_BLOCK_SIZE];
        
buffer for writing block data headers /** buffer for writing block data headers */
        private final byte[] hbuf = new byte[MAX_HEADER_SIZE];
        
char buffer for fast string writes /** char buffer for fast string writes */
        private final char[] cbuf = new char[CHAR_BUF_SIZE];

        
block data mode /** block data mode */
        private boolean blkmode = false;
        
current offset into buf /** current offset into buf */
        private int pos = 0;

        
underlying output stream /** underlying output stream */
        private final OutputStream out;
        
loopback stream (for data writes that span data blocks) /** loopback stream (for data writes that span data blocks) */
        private final DataOutputStream dout;

        
Creates new BlockDataOutputStream on top of given underlying stream.
Block data mode is turned off by default.
/**
         * Creates new BlockDataOutputStream on top of given underlying stream.
         * Block data mode is turned off by default.
         */
        BlockDataOutputStream(OutputStream out) {
            this.out = out;
            dout = new DataOutputStream(this);
        }

        
Sets block data mode to the given mode (true == on, false == off)
and returns the previous mode value.  If the new mode is the same as
the old mode, no action is taken.  If the new mode differs from the
old mode, any buffered data is flushed before switching to the new
mode.
/**
         * Sets block data mode to the given mode (true == on, false == off)
         * and returns the previous mode value.  If the new mode is the same as
         * the old mode, no action is taken.  If the new mode differs from the
         * old mode, any buffered data is flushed before switching to the new
         * mode.
         */
        boolean setBlockDataMode(boolean mode) throws IOException {
            if (blkmode == mode) {
                return blkmode;
            }
            drain();
            blkmode = mode;
            return !blkmode;
        }

        
Returns true if the stream is currently in block data mode, false
otherwise.
/**
         * Returns true if the stream is currently in block data mode, false
         * otherwise.
         */
        boolean getBlockDataMode() {
            return blkmode;
        }

        /* ----------------- generic output stream methods ----------------- */
        /*
         * The following methods are equivalent to their counterparts in
         * OutputStream, except that they partition written data into data
         * blocks when in block data mode.
         */

        public void write(int b) throws IOException {
            if (pos >= MAX_BLOCK_SIZE) {
                drain();
            }
            buf[pos++] = (byte) b;
        }

        public void write(byte[] b) throws IOException {
            write(b, 0, b.length, false);
        }

        public void write(byte[] b, int off, int len) throws IOException {
            write(b, off, len, false);
        }

        public void flush() throws IOException {
            drain();
            out.flush();
        }

        public void close() throws IOException {
            flush();
            out.close();
        }

        
Writes specified span of byte values from given array.  If copy is
true, copies the values to an intermediate buffer before writing
them to underlying stream (to avoid exposing a reference to the
original byte array).
/**
         * Writes specified span of byte values from given array.  If copy is
         * true, copies the values to an intermediate buffer before writing
         * them to underlying stream (to avoid exposing a reference to the
         * original byte array).
         */
        void write(byte[] b, int off, int len, boolean copy)
            throws IOException
        {
            if (!(copy || blkmode)) {           // write directly
                drain();
                out.write(b, off, len);
                return;
            }

            while (len > 0) {
                if (pos >= MAX_BLOCK_SIZE) {
                    drain();
                }
                if (len >= MAX_BLOCK_SIZE && !copy && pos == 0) {
                    // avoid unnecessary copy
                    writeBlockHeader(MAX_BLOCK_SIZE);
                    out.write(b, off, MAX_BLOCK_SIZE);
                    off += MAX_BLOCK_SIZE;
                    len -= MAX_BLOCK_SIZE;
                } else {
                    int wlen = Math.min(len, MAX_BLOCK_SIZE - pos);
                    System.arraycopy(b, off, buf, pos, wlen);
                    pos += wlen;
                    off += wlen;
                    len -= wlen;
                }
            }
        }

        
Writes all buffered data from this stream to the underlying stream,
but does not flush underlying stream.
/**
         * Writes all buffered data from this stream to the underlying stream,
         * but does not flush underlying stream.
         */
        void drain() throws IOException {
            if (pos == 0) {
                return;
            }
            if (blkmode) {
                writeBlockHeader(pos);
            }
            out.write(buf, 0, pos);
            pos = 0;
        }

        
Writes block data header.  Data blocks shorter than 256 bytes are
prefixed with a 2-byte header; all others start with a 5-byte
header.
/**
         * Writes block data header.  Data blocks shorter than 256 bytes are
         * prefixed with a 2-byte header; all others start with a 5-byte
         * header.
         */
        private void writeBlockHeader(int len) throws IOException {
            if (len <= 0xFF) {
                hbuf[0] = TC_BLOCKDATA;
                hbuf[1] = (byte) len;
                out.write(hbuf, 0, 2);
            } else {
                hbuf[0] = TC_BLOCKDATALONG;
                Bits.putInt(hbuf, 1, len);
                out.write(hbuf, 0, 5);
            }
        }


        /* ----------------- primitive data output methods ----------------- */
        /*
         * The following methods are equivalent to their counterparts in
         * DataOutputStream, except that they partition written data into data
         * blocks when in block data mode.
         */

        public void writeBoolean(boolean v) throws IOException {
            if (pos >= MAX_BLOCK_SIZE) {
                drain();
            }
            Bits.putBoolean(buf, pos++, v);
        }

        public void writeByte(int v) throws IOException {
            if (pos >= MAX_BLOCK_SIZE) {
                drain();
            }
            buf[pos++] = (byte) v;
        }

        public void writeChar(int v) throws IOException {
            if (pos + 2 <= MAX_BLOCK_SIZE) {
                Bits.putChar(buf, pos, (char) v);
                pos += 2;
            } else {
                dout.writeChar(v);
            }
        }

        public void writeShort(int v) throws IOException {
            if (pos + 2 <= MAX_BLOCK_SIZE) {
                Bits.putShort(buf, pos, (short) v);
                pos += 2;
            } else {
                dout.writeShort(v);
            }
        }

        public void writeInt(int v) throws IOException {
            if (pos + 4 <= MAX_BLOCK_SIZE) {
                Bits.putInt(buf, pos, v);
                pos += 4;
            } else {
                dout.writeInt(v);
            }
        }

        public void writeFloat(float v) throws IOException {
            if (pos + 4 <= MAX_BLOCK_SIZE) {
                Bits.putFloat(buf, pos, v);
                pos += 4;
            } else {
                dout.writeFloat(v);
            }
        }

        public void writeLong(long v) throws IOException {
            if (pos + 8 <= MAX_BLOCK_SIZE) {
                Bits.putLong(buf, pos, v);
                pos += 8;
            } else {
                dout.writeLong(v);
            }
        }

        public void writeDouble(double v) throws IOException {
            if (pos + 8 <= MAX_BLOCK_SIZE) {
                Bits.putDouble(buf, pos, v);
                pos += 8;
            } else {
                dout.writeDouble(v);
            }
        }

        public void writeBytes(String s) throws IOException {
            int endoff = s.length();
            int cpos = 0;
            int csize = 0;
            for (int off = 0; off < endoff; ) {
                if (cpos >= csize) {
                    cpos = 0;
                    csize = Math.min(endoff - off, CHAR_BUF_SIZE);
                    s.getChars(off, off + csize, cbuf, 0);
                }
                if (pos >= MAX_BLOCK_SIZE) {
                    drain();
                }
                int n = Math.min(csize - cpos, MAX_BLOCK_SIZE - pos);
                int stop = pos + n;
                while (pos < stop) {
                    buf[pos++] = (byte) cbuf[cpos++];
                }
                off += n;
            }
        }

        public void writeChars(String s) throws IOException {
            int endoff = s.length();
            for (int off = 0; off < endoff; ) {
                int csize = Math.min(endoff - off, CHAR_BUF_SIZE);
                s.getChars(off, off + csize, cbuf, 0);
                writeChars(cbuf, 0, csize);
                off += csize;
            }
        }

        public void writeUTF(String s) throws IOException {
            writeUTF(s, getUTFLength(s));
        }


        /* -------------- primitive data array output methods -------------- */
        /*
         * The following methods write out spans of primitive data values.
         * Though equivalent to calling the corresponding primitive write
         * methods repeatedly, these methods are optimized for writing groups
         * of primitive data values more efficiently.
         */

        void writeBooleans(boolean[] v, int off, int len) throws IOException {
            int endoff = off + len;
            while (off < endoff) {
                if (pos >= MAX_BLOCK_SIZE) {
                    drain();
                }
                int stop = Math.min(endoff, off + (MAX_BLOCK_SIZE - pos));
                while (off < stop) {
                    Bits.putBoolean(buf, pos++, v[off++]);
                }
            }
        }

        void writeChars(char[] v, int off, int len) throws IOException {
            int limit = MAX_BLOCK_SIZE - 2;
            int endoff = off + len;
            while (off < endoff) {
                if (pos <= limit) {
                    int avail = (MAX_BLOCK_SIZE - pos) >> 1;
                    int stop = Math.min(endoff, off + avail);
                    while (off < stop) {
                        Bits.putChar(buf, pos, v[off++]);
                        pos += 2;
                    }
                } else {
                    dout.writeChar(v[off++]);
                }
            }
        }

        void writeShorts(short[] v, int off, int len) throws IOException {
            int limit = MAX_BLOCK_SIZE - 2;
            int endoff = off + len;
            while (off < endoff) {
                if (pos <= limit) {
                    int avail = (MAX_BLOCK_SIZE - pos) >> 1;
                    int stop = Math.min(endoff, off + avail);
                    while (off < stop) {
                        Bits.putShort(buf, pos, v[off++]);
                        pos += 2;
                    }
                } else {
                    dout.writeShort(v[off++]);
                }
            }
        }

        void writeInts(int[] v, int off, int len) throws IOException {
            int limit = MAX_BLOCK_SIZE - 4;
            int endoff = off + len;
            while (off < endoff) {
                if (pos <= limit) {
                    int avail = (MAX_BLOCK_SIZE - pos) >> 2;
                    int stop = Math.min(endoff, off + avail);
                    while (off < stop) {
                        Bits.putInt(buf, pos, v[off++]);
                        pos += 4;
                    }
                } else {
                    dout.writeInt(v[off++]);
                }
            }
        }

        void writeFloats(float[] v, int off, int len) throws IOException {
            int limit = MAX_BLOCK_SIZE - 4;
            int endoff = off + len;
            while (off < endoff) {
                if (pos <= limit) {
                    int avail = (MAX_BLOCK_SIZE - pos) >> 2;
                    int chunklen = Math.min(endoff - off, avail);
                    floatsToBytes(v, off, buf, pos, chunklen);
                    off += chunklen;
                    pos += chunklen << 2;
                } else {
                    dout.writeFloat(v[off++]);
                }
            }
        }

        void writeLongs(long[] v, int off, int len) throws IOException {
            int limit = MAX_BLOCK_SIZE - 8;
            int endoff = off + len;
            while (off < endoff) {
                if (pos <= limit) {
                    int avail = (MAX_BLOCK_SIZE - pos) >> 3;
                    int stop = Math.min(endoff, off + avail);
                    while (off < stop) {
                        Bits.putLong(buf, pos, v[off++]);
                        pos += 8;
                    }
                } else {
                    dout.writeLong(v[off++]);
                }
            }
        }

        void writeDoubles(double[] v, int off, int len) throws IOException {
            int limit = MAX_BLOCK_SIZE - 8;
            int endoff = off + len;
            while (off < endoff) {
                if (pos <= limit) {
                    int avail = (MAX_BLOCK_SIZE - pos) >> 3;
                    int chunklen = Math.min(endoff - off, avail);
                    doublesToBytes(v, off, buf, pos, chunklen);
                    off += chunklen;
                    pos += chunklen << 3;
                } else {
                    dout.writeDouble(v[off++]);
                }
            }
        }

        
Returns the length in bytes of the UTF encoding of the given string.
/**
         * Returns the length in bytes of the UTF encoding of the given string.
         */
        long getUTFLength(String s) {
            int len = s.length();
            long utflen = 0;
            for (int off = 0; off < len; ) {
                int csize = Math.min(len - off, CHAR_BUF_SIZE);
                s.getChars(off, off + csize, cbuf, 0);
                for (int cpos = 0; cpos < csize; cpos++) {
                    char c = cbuf[cpos];
                    if (c >= 0x0001 && c <= 0x007F) {
                        utflen++;
                    } else if (c > 0x07FF) {
                        utflen += 3;
                    } else {
                        utflen += 2;
                    }
                }
                off += csize;
            }
            return utflen;
        }

        
Writes the given string in UTF format.  This method is used in
situations where the UTF encoding length of the string is already
known; specifying it explicitly avoids a prescan of the string to
determine its UTF length.
/**
         * Writes the given string in UTF format.  This method is used in
         * situations where the UTF encoding length of the string is already
         * known; specifying it explicitly avoids a prescan of the string to
         * determine its UTF length.
         */
        void writeUTF(String s, long utflen) throws IOException {
            if (utflen > 0xFFFFL) {
                throw new UTFDataFormatException();
            }
            writeShort((int) utflen);
            if (utflen == (long) s.length()) {
                writeBytes(s);
            } else {
                writeUTFBody(s);
            }
        }

        
Writes given string in "long" UTF format.  "Long" UTF format is
identical to standard UTF, except that it uses an 8 byte header
(instead of the standard 2 bytes) to convey the UTF encoding length.
/**
         * Writes given string in "long" UTF format.  "Long" UTF format is
         * identical to standard UTF, except that it uses an 8 byte header
         * (instead of the standard 2 bytes) to convey the UTF encoding length.
         */
        void writeLongUTF(String s) throws IOException {
            writeLongUTF(s, getUTFLength(s));
        }

        
Writes given string in "long" UTF format, where the UTF encoding
length of the string is already known.
/**
         * Writes given string in "long" UTF format, where the UTF encoding
         * length of the string is already known.
         */
        void writeLongUTF(String s, long utflen) throws IOException {
            writeLong(utflen);
            if (utflen == (long) s.length()) {
                writeBytes(s);
            } else {
                writeUTFBody(s);
            }
        }

        
Writes the "body" (i.e., the UTF representation minus the 2-byte or
8-byte length header) of the UTF encoding for the given string.
/**
         * Writes the "body" (i.e., the UTF representation minus the 2-byte or
         * 8-byte length header) of the UTF encoding for the given string.
         */
        private void writeUTFBody(String s) throws IOException {
            int limit = MAX_BLOCK_SIZE - 3;
            int len = s.length();
            for (int off = 0; off < len; ) {
                int csize = Math.min(len - off, CHAR_BUF_SIZE);
                s.getChars(off, off + csize, cbuf, 0);
                for (int cpos = 0; cpos < csize; cpos++) {
                    char c = cbuf[cpos];
                    if (pos <= limit) {
                        if (c <= 0x007F && c != 0) {
                            buf[pos++] = (byte) c;
                        } else if (c > 0x07FF) {
                            buf[pos + 2] = (byte) (0x80 | ((c >> 0) & 0x3F));
                            buf[pos + 1] = (byte) (0x80 | ((c >> 6) & 0x3F));
                            buf[pos + 0] = (byte) (0xE0 | ((c >> 12) & 0x0F));
                            pos += 3;
                        } else {
                            buf[pos + 1] = (byte) (0x80 | ((c >> 0) & 0x3F));
                            buf[pos + 0] = (byte) (0xC0 | ((c >> 6) & 0x1F));
                            pos += 2;
                        }
                    } else {    // write one byte at a time to normalize block
                        if (c <= 0x007F && c != 0) {
                            write(c);
                        } else if (c > 0x07FF) {
                            write(0xE0 | ((c >> 12) & 0x0F));
                            write(0x80 | ((c >> 6) & 0x3F));
                            write(0x80 | ((c >> 0) & 0x3F));
                        } else {
                            write(0xC0 | ((c >> 6) & 0x1F));
                            write(0x80 | ((c >> 0) & 0x3F));
                        }
                    }
                }
                off += csize;
            }
        }
    }

    
Lightweight identity hash table which maps objects to integer handles,
assigned in ascending order.
/**
     * Lightweight identity hash table which maps objects to integer handles,
     * assigned in ascending order.
     */
    private static class HandleTable {

        /* number of mappings in table/next available handle */
        private int size;
        /* size threshold determining when to expand hash spine */
        private int threshold;
        /* factor for computing size threshold */
        private final float loadFactor;
        /* maps hash value -> candidate handle value */
        private int[] spine;
        /* maps handle value -> next candidate handle value */
        private int[] next;
        /* maps handle value -> associated object */
        private Object[] objs;

        
Creates new HandleTable with given capacity and load factor.
/**
         * Creates new HandleTable with given capacity and load factor.
         */
        HandleTable(int initialCapacity, float loadFactor) {
            this.loadFactor = loadFactor;
            spine = new int[initialCapacity];
            next = new int[initialCapacity];
            objs = new Object[initialCapacity];
            threshold = (int) (initialCapacity * loadFactor);
            clear();
        }

        
Assigns next available handle to given object, and returns handle
value.  Handles are assigned in ascending order starting at 0.
/**
         * Assigns next available handle to given object, and returns handle
         * value.  Handles are assigned in ascending order starting at 0.
         */
        int assign(Object obj) {
            if (size >= next.length) {
                growEntries();
            }
            if (size >= threshold) {
                growSpine();
            }
            insert(obj, size);
            return size++;
        }

        
Looks up and returns handle associated with given object, or -1 if
no mapping found.
/**
         * Looks up and returns handle associated with given object, or -1 if
         * no mapping found.
         */
        int lookup(Object obj) {
            if (size == 0) {
                return -1;
            }
            int index = hash(obj) % spine.length;
            for (int i = spine[index]; i >= 0; i = next[i]) {
                if (objs[i] == obj) {
                    return i;
                }
            }
            return -1;
        }

        
Resets table to its initial (empty) state.
/**
         * Resets table to its initial (empty) state.
         */
        void clear() {
            Arrays.fill(spine, -1);
            Arrays.fill(objs, 0, size, null);
            size = 0;
        }

        
Returns the number of mappings currently in table.
/**
         * Returns the number of mappings currently in table.
         */
        int size() {
            return size;
        }

        
Inserts mapping object -> handle mapping into table.  Assumes table
is large enough to accommodate new mapping.
/**
         * Inserts mapping object -> handle mapping into table.  Assumes table
         * is large enough to accommodate new mapping.
         */
        private void insert(Object obj, int handle) {
            int index = hash(obj) % spine.length;
            objs[handle] = obj;
            next[handle] = spine[index];
            spine[index] = handle;
        }

        
Expands the hash "spine" -- equivalent to increasing the number of
buckets in a conventional hash table.
/**
         * Expands the hash "spine" -- equivalent to increasing the number of
         * buckets in a conventional hash table.
         */
        private void growSpine() {
            spine = new int[(spine.length << 1) + 1];
            threshold = (int) (spine.length * loadFactor);
            Arrays.fill(spine, -1);
            for (int i = 0; i < size; i++) {
                insert(objs[i], i);
            }
        }

        
Increases hash table capacity by lengthening entry arrays.
/**
         * Increases hash table capacity by lengthening entry arrays.
         */
        private void growEntries() {
            int newLength = (next.length << 1) + 1;
            int[] newNext = new int[newLength];
            System.arraycopy(next, 0, newNext, 0, size);
            next = newNext;

            Object[] newObjs = new Object[newLength];
            System.arraycopy(objs, 0, newObjs, 0, size);
            objs = newObjs;
        }

        
Returns hash value for given object.
/**
         * Returns hash value for given object.
         */
        private int hash(Object obj) {
            return System.identityHashCode(obj) & 0x7FFFFFFF;
        }
    }

    
Lightweight identity hash table which maps objects to replacement
objects.
/**
     * Lightweight identity hash table which maps objects to replacement
     * objects.
     */
    private static class ReplaceTable {

        /* maps object -> index */
        private final HandleTable htab;
        /* maps index -> replacement object */
        private Object[] reps;

        
Creates new ReplaceTable with given capacity and load factor.
/**
         * Creates new ReplaceTable with given capacity and load factor.
         */
        ReplaceTable(int initialCapacity, float loadFactor) {
            htab = new HandleTable(initialCapacity, loadFactor);
            reps = new Object[initialCapacity];
        }

        
Enters mapping from object to replacement object.
/**
         * Enters mapping from object to replacement object.
         */
        void assign(Object obj, Object rep) {
            int index = htab.assign(obj);
            while (index >= reps.length) {
                grow();
            }
            reps[index] = rep;
        }

        
Looks up and returns replacement for given object.  If no
replacement is found, returns the lookup object itself.
/**
         * Looks up and returns replacement for given object.  If no
         * replacement is found, returns the lookup object itself.
         */
        Object lookup(Object obj) {
            int index = htab.lookup(obj);
            return (index >= 0) ? reps[index] : obj;
        }

        
Resets table to its initial (empty) state.
/**
         * Resets table to its initial (empty) state.
         */
        void clear() {
            Arrays.fill(reps, 0, htab.size(), null);
            htab.clear();
        }

        
Returns the number of mappings currently in table.
/**
         * Returns the number of mappings currently in table.
         */
        int size() {
            return htab.size();
        }

        
Increases table capacity.
/**
         * Increases table capacity.
         */
        private void grow() {
            Object[] newReps = new Object[(reps.length << 1) + 1];
            System.arraycopy(reps, 0, newReps, 0, reps.length);
            reps = newReps;
        }
    }

    
Stack to keep debug information about the state of the
serialization process, for embedding in exception messages.
/**
     * Stack to keep debug information about the state of the
     * serialization process, for embedding in exception messages.
     */
    private static class DebugTraceInfoStack {
        private final List<String> stack;

        DebugTraceInfoStack() {
            stack = new ArrayList<>();
        }

        
Removes all of the elements from enclosed list.
/**
         * Removes all of the elements from enclosed list.
         */
        void clear() {
            stack.clear();
        }

        
Removes the object at the top of enclosed list.
/**
         * Removes the object at the top of enclosed list.
         */
        void pop() {
            stack.remove(stack.size()-1);
        }

        
Pushes a String onto the top of enclosed list.
/**
         * Pushes a String onto the top of enclosed list.
         */
        void push(String entry) {
            stack.add("\t- " + entry);
        }

        
Returns a string representation of this object
/**
         * Returns a string representation of this object
         */
        public String toString() {
            StringJoiner sj = new StringJoiner("\n");
            for (int i = stack.size() - 1; i >= 0; i--) {
                sj.add(stack.get(i));
            }
            return sj.toString();
        }
    }

}