http://www.javassist.org/: Javassist (JAVA programming ASSISTant) makes Java bytecode manipulation simple. It is a class library for editing bytecodes in Java. (Shigeru Chiba, www.javassist.org) 
/*
 * Javassist, a Java-bytecode translator toolkit.
 * Copyright (C) 1999- Shigeru Chiba. All Rights Reserved.
 *
 * The contents of this file are subject to the Mozilla Public License Version
 * 1.1 (the "License"); you may not use this file except in compliance with
 * the License.  Alternatively, the contents of this file may be used under
 * the terms of the GNU Lesser General Public License Version 2.1 or later,
 * or the Apache License Version 2.0.
 *
 * Software distributed under the License is distributed on an "AS IS" basis,
 * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
 * for the specific language governing rights and limitations under the
 * License.
 */

package javassist.bytecode;

import java.util.ArrayList;
import java.util.List;


An iterator for editing a code attribute.

To directly read or edit a bytecode sequence, call byteAt(int), s16bitAt(int), writeByte(int, int), write16bit(int, int), and other methods. For example, if method refers to a CtMethod object,
the following code substitutes the NOP instruction for the first
instruction of the method:  

CodeAttribute ca = method.getMethodInfo().getCodeAttribute();
CodeIterator ci = ca.iterator();
ci.writeByte(Opcode.NOP, 0);


To visit every instruction, call next() on a CodeIterator.
It returns the index of the first byte of the next instruction.

If there are multiple CodeIterators referring to the
same Code_attribute, then inserting a gap by one
CodeIterator will break the other
CodeIterator.

This iterator does not provide remove().
If a piece of code in a Code_attribute is unnecessary,
it should be overwritten with NOP.

See Also:
/**
 * An iterator for editing a code attribute.
 *
 * <p>To directly read or edit a bytecode sequence, call {@link #byteAt(int)}, {@link #s16bitAt(int)},
 * {@link #writeByte(int, int)}, {@link #write16bit(int, int)}, and other methods.
 * For example, if <code>method</code> refers to a <code>CtMethod</code> object,
 * the following code substitutes the <code>NOP</code> instruction for the first
 * instruction of the method:  
 *
 * <pre>
 * CodeAttribute ca = method.getMethodInfo().getCodeAttribute();
 * CodeIterator ci = ca.iterator();
 * ci.writeByte(Opcode.NOP, 0);</pre>
 *
 * <p>To visit every instruction, call {@link #next()} on a <code>CodeIterator</code>.
 * It returns the index of the first byte of the next instruction.
 *
 * <p>If there are multiple <code>CodeIterator</code>s referring to the
 * same <code>Code_attribute</code>, then inserting a gap by one
 * <code>CodeIterator</code> will break the other
 * <code>CodeIterator</code>.
 *
 * <p>This iterator does not provide <code>remove()</code>.
 * If a piece of code in a <code>Code_attribute</code> is unnecessary,
 * it should be overwritten with <code>NOP</code>.
 *
 * @see CodeAttribute#iterator()
 */
public class CodeIterator implements Opcode {
    protected CodeAttribute codeAttr;
    protected byte[] bytecode;
    protected int endPos;
    protected int currentPos;
    protected int mark, mark2;

    protected CodeIterator(CodeAttribute ca) {
        codeAttr = ca;
        bytecode = ca.getCode();
        begin();
    }

    
Moves to the first instruction.

/**
     * Moves to the first instruction.
     */
    public void begin() {
        currentPos = mark = mark2 = 0;
        endPos = getCodeLength();
    }

    
Moves to the given index.

The index of the next instruction is set to the given index.
The successive call to next()
returns the index that has been given to move().

Note that the index is into the byte array returned by
get().getCode().

See Also:
  • getCode.getCode()
/**
     * Moves to the given index.
     *
     * <p>The index of the next instruction is set to the given index.
     * The successive call to <code>next()</code>
     * returns the index that has been given to <code>move()</code>.
     *
     * <p>Note that the index is into the byte array returned by
     * <code>get().getCode()</code>.
     *
     * @see CodeAttribute#getCode()
     */
    public void move(int index) {
        currentPos = index;
    }

    
Sets a mark to the bytecode at the given index.
The mark can be used to track the position of that bytecode
when code blocks are inserted.
If a code block is inclusively inserted at the position of the
bytecode, the mark is set to the inserted code block.

See Also:
  • getMark()
Since:3.11
/**
     * Sets a mark to the bytecode at the given index.
     * The mark can be used to track the position of that bytecode
     * when code blocks are inserted.
     * If a code block is inclusively inserted at the position of the
     * bytecode, the mark is set to the inserted code block.
     *
     * @see #getMark()
     * @since 3.11
     */
    public void setMark(int index) {
        mark = index;
    }

    
Sets a mark to the bytecode at the given index.
The mark can be used to track the position of that bytecode
when code blocks are inserted.
If a code block is inclusively inserted at the position of the
bytecode, the mark is set to the inserted code block.

See Also:
  • getMark2()
Since:3.26
/**
     * Sets a mark to the bytecode at the given index.
     * The mark can be used to track the position of that bytecode
     * when code blocks are inserted.
     * If a code block is inclusively inserted at the position of the
     * bytecode, the mark is set to the inserted code block.
     *
     * @see #getMark2()
     * @since 3.26
     */
    public void setMark2(int index) {
        mark2 = index;
    }

    
Gets the index of the position of the mark set by
setMark.

See Also:
Returns:the index of the position.
Since:3.11
/**
     * Gets the index of the position of the mark set by
     * <code>setMark</code>.
     *
     * @return the index of the position.
     * @see #setMark(int)
     * @since 3.11
     */
    public int getMark() { return mark; }

    
Gets the index of the position of the mark set by
setMark2.

See Also:
Returns:the index of the position.
Since:3.26
/**
     * Gets the index of the position of the mark set by
     * <code>setMark2</code>.
     *
     * @return the index of the position.
     * @see #setMark2(int)
     * @since 3.26
     */
    public int getMark2() { return mark2; }

    
Returns a Code attribute read with this iterator.

/**
     * Returns a Code attribute read with this iterator.
     */
    public CodeAttribute get() {
        return codeAttr;
    }

    
Returns code_length of Code_attribute.

/**
     * Returns <code>code_length</code> of <code>Code_attribute</code>.
     */
    public int getCodeLength() {
        return bytecode.length;
    }

    
Returns the unsigned 8bit value at the given index.

/**
     * Returns the unsigned 8bit value at the given index.
     */
    public int byteAt(int index) { return bytecode[index] & 0xff; }

    
Returns the signed 8bit value at the given index.

/**
     * Returns the signed 8bit value at the given index.
     */
    public int signedByteAt(int index) { return bytecode[index]; }

    
Writes an 8bit value at the given index.

/**
     * Writes an 8bit value at the given index.
     */
    public void writeByte(int value, int index) {
        bytecode[index] = (byte)value;
    }

    
Returns the unsigned 16bit value at the given index.

/**
     * Returns the unsigned 16bit value at the given index.
     */
    public int u16bitAt(int index) {
        return ByteArray.readU16bit(bytecode, index);
    }

    
Returns the signed 16bit value at the given index.

/**
     * Returns the signed 16bit value at the given index.
     */
    public int s16bitAt(int index) {
        return ByteArray.readS16bit(bytecode, index);
    }

    
Writes a 16 bit integer at the index.

/**
     * Writes a 16 bit integer at the index.
     */
    public void write16bit(int value, int index) {
        ByteArray.write16bit(value, bytecode, index);
    }

    
Returns the signed 32bit value at the given index.

/**
     * Returns the signed 32bit value at the given index.
     */
    public int s32bitAt(int index) {
        return ByteArray.read32bit(bytecode, index);
    }

    
Writes a 32bit integer at the index.

/**
     * Writes a 32bit integer at the index.
     */
    public void write32bit(int value, int index) {
        ByteArray.write32bit(value, bytecode, index);
    }

    
Writes a byte array at the index.

Params:
  • code – 	may be a zero-length array.
/**
     * Writes a byte array at the index.
     *
     * @param code	may be a zero-length array.
     */
    public void write(byte[] code, int index) {
        int len = code.length;
        for (int j = 0; j < len; ++j)
            bytecode[index++] = code[j];
    }

    
Returns true if there is more instructions.

/**
     * Returns true if there is more instructions.
     */
    public boolean hasNext() { return currentPos < endPos; }

    
Returns the index of the next instruction
(not the operand following the current opcode).

Note that the index is into the byte array returned by
get().getCode().

See Also:
/**
     * Returns the index of the next instruction
     * (not the operand following the current opcode).
     *
     * <p>Note that the index is into the byte array returned by
     * <code>get().getCode()</code>.
     *
     * @see CodeAttribute#getCode()
     * @see CodeIterator#byteAt(int)
     */
    public int next() throws BadBytecode {
        int pos = currentPos;
        currentPos = nextOpcode(bytecode, pos);
        return pos;
    }

    
Obtains the value that the next call
to next() will return.

This method is side-effects free.
Successive calls to lookAhead() return the
same value until next() is called.

/**
     * Obtains the value that the next call
     * to <code>next()</code> will return.
     *
     * <p>This method is side-effects free.
     * Successive calls to <code>lookAhead()</code> return the
     * same value until <code>next()</code> is called.
     */
    public int lookAhead() {
        return currentPos;
    }

    
Moves to the instruction for
either super() or this().

This method skips all the instructions for computing arguments
to super() or this(), which should be
placed at the beginning of a constructor body.

This method returns the index of INVOKESPECIAL instruction
executing super() or this().
A successive call to next() returns the
index of the next instruction following that INVOKESPECIAL.

This method works only for a constructor.

Returns: the index of the INVOKESPECIAL instruction, or -1
         if a constructor invocation is not found.
/**
     * Moves to the instruction for
     * either <code>super()</code> or <code>this()</code>.
     *
     * <p>This method skips all the instructions for computing arguments
     * to <code>super()</code> or <code>this()</code>, which should be
     * placed at the beginning of a constructor body.
     *
     * <p>This method returns the index of INVOKESPECIAL instruction
     * executing <code>super()</code> or <code>this()</code>.
     * A successive call to <code>next()</code> returns the
     * index of the next instruction following that INVOKESPECIAL.
     *
     * <p>This method works only for a constructor.
     *
     * @return  the index of the INVOKESPECIAL instruction, or -1
     *          if a constructor invocation is not found.
     */
    public int skipConstructor() throws BadBytecode {
        return skipSuperConstructor0(-1);
    }

    
Moves to the instruction for super().

This method skips all the instructions for computing arguments to
super(), which should be
placed at the beginning of a constructor body.

This method returns the index of INVOKESPECIAL instruction
executing super().
A successive call to next() returns the
index of the next instruction following that INVOKESPECIAL.

This method works only for a constructor.

Returns: the index of the INVOKESPECIAL instruction, or -1
         if a super constructor invocation is not found
         but this() is found.
/**
     * Moves to the instruction for <code>super()</code>.
     *
     * <p>This method skips all the instructions for computing arguments to
     * <code>super()</code>, which should be
     * placed at the beginning of a constructor body.
     *
     * <p>This method returns the index of INVOKESPECIAL instruction
     * executing <code>super()</code>.
     * A successive call to <code>next()</code> returns the
     * index of the next instruction following that INVOKESPECIAL.
     *
     * <p>This method works only for a constructor.
     *
     * @return  the index of the INVOKESPECIAL instruction, or -1
     *          if a super constructor invocation is not found
     *          but <code>this()</code> is found.
     */
    public int skipSuperConstructor() throws BadBytecode {
        return skipSuperConstructor0(0);
    }

    
Moves to the instruction for this().

This method skips all the instructions for computing arguments to
this(), which should be
placed at the beginning of a constructor body.

This method returns the index of INVOKESPECIAL instruction
executing this().
A successive call to next() returns the
index of the next instruction following that INVOKESPECIAL.

This method works only for a constructor.

Returns: the index of the INVOKESPECIAL instruction, or -1
         if a explicit constructor invocation is not found
         but super() is found.
/**
     * Moves to the instruction for <code>this()</code>.
     *
     * <p>This method skips all the instructions for computing arguments to
     * <code>this()</code>, which should be
     * placed at the beginning of a constructor body.
     *
     * <p>This method returns the index of INVOKESPECIAL instruction
     * executing <code>this()</code>.
     * A successive call to <code>next()</code> returns the
     * index of the next instruction following that INVOKESPECIAL.
     *
     * <p>This method works only for a constructor.
     *
     * @return  the index of the INVOKESPECIAL instruction, or -1
     *          if a explicit constructor invocation is not found
     *          but <code>super()</code> is found.
     */
    public int skipThisConstructor() throws BadBytecode {
        return skipSuperConstructor0(1);
    }

    /* skipSuper        1: this(), 0: super(), -1: both.
     */
    private int skipSuperConstructor0(int skipThis) throws BadBytecode {
        begin();
        ConstPool cp = codeAttr.getConstPool();
        String thisClassName = codeAttr.getDeclaringClass();
        int nested = 0;
        while (hasNext()) {
            int index = next();
            int c = byteAt(index);
            if (c == NEW)
                ++nested;
            else if (c == INVOKESPECIAL) {
                int mref = ByteArray.readU16bit(bytecode, index + 1);
                if (cp.getMethodrefName(mref).equals(MethodInfo.nameInit))
                    if (--nested < 0) {
                        if (skipThis < 0)
                            return index;

                        String cname = cp.getMethodrefClassName(mref);
                        if (cname.equals(thisClassName) == (skipThis > 0))
                            return index;

                        break;
                    }
            }
        }

        begin();
        return -1;
    }

    
Inserts the given bytecode sequence
before the next instruction that would be returned by
next() (not before the instruction returned
by the last call to next()).
Branch offsets and the exception table are also updated.

If the next instruction is at the beginning of a block statement,
then the bytecode is inserted within that block.

An extra gap may be inserted at the end of the inserted
bytecode sequence for adjusting alignment if the code attribute
includes LOOKUPSWITCH or TABLESWITCH.

Params:
  • code –      inserted bytecode sequence.
Returns:         the index indicating the first byte of the
                 inserted byte sequence.
/**
     * Inserts the given bytecode sequence
     * before the next instruction that would be returned by
     * <code>next()</code> (not before the instruction returned
     * by the last call to <code>next()</code>).
     * Branch offsets and the exception table are also updated.
     *
     * <p>If the next instruction is at the beginning of a block statement,
     * then the bytecode is inserted within that block.
     *
     * <p>An extra gap may be inserted at the end of the inserted
     * bytecode sequence for adjusting alignment if the code attribute
     * includes <code>LOOKUPSWITCH</code> or <code>TABLESWITCH</code>.
     *
     * @param code      inserted bytecode sequence.
     * @return          the index indicating the first byte of the
     *                  inserted byte sequence.
     */
    public int insert(byte[] code)
        throws BadBytecode
    {
        return insert0(currentPos, code, false);
    }

    
Inserts the given bytecode sequence
before the instruction at the given index pos.
Branch offsets and the exception table are also updated.

If the instruction at the given index is at the beginning
of a block statement,
then the bytecode is inserted within that block.

An extra gap may be inserted at the end of the inserted
bytecode sequence for adjusting alignment if the code attribute
includes LOOKUPSWITCH or TABLESWITCH.

The index at which the byte sequence is actually inserted
might be different from pos since some other bytes might be
inserted at other positions (e.g. to change GOTO
to GOTO_W).

Params:
  • pos –       the index at which a byte sequence is inserted.
  • code –      inserted bytecode sequence.
/**
     * Inserts the given bytecode sequence
     * before the instruction at the given index <code>pos</code>.
     * Branch offsets and the exception table are also updated.
     *
     * <p>If the instruction at the given index is at the beginning
     * of a block statement,
     * then the bytecode is inserted within that block.
     *
     * <p>An extra gap may be inserted at the end of the inserted
     * bytecode sequence for adjusting alignment if the code attribute
     * includes <code>LOOKUPSWITCH</code> or <code>TABLESWITCH</code>.
     *
     * <p>The index at which the byte sequence is actually inserted
     * might be different from pos since some other bytes might be
     * inserted at other positions (e.g. to change <code>GOTO</code>
     * to <code>GOTO_W</code>).
     *
     * @param pos       the index at which a byte sequence is inserted.
     * @param code      inserted bytecode sequence.
     */
    public void insert(int pos, byte[] code) throws BadBytecode {
        insert0(pos, code, false);
    }

    
Inserts the given bytecode sequence
before the instruction at the given index pos.
Branch offsets and the exception table are also updated.

If the instruction at the given index is at the beginning
of a block statement,
then the bytecode is inserted within that block.

An extra gap may be inserted at the end of the inserted
bytecode sequence for adjusting alignment if the code attribute
includes LOOKUPSWITCH or TABLESWITCH.

Params:
  • pos –       the index at which a byte sequence is inserted.
  • code –      inserted bytecode sequence.
Returns:         the index indicating the first byte of the
                 inserted byte sequence, which might be
                 different from pos.
Since:3.11
/**
     * Inserts the given bytecode sequence
     * before the instruction at the given index <code>pos</code>.
     * Branch offsets and the exception table are also updated.
     *
     * <p>If the instruction at the given index is at the beginning
     * of a block statement,
     * then the bytecode is inserted within that block.
     *
     * <p>An extra gap may be inserted at the end of the inserted
     * bytecode sequence for adjusting alignment if the code attribute
     * includes <code>LOOKUPSWITCH</code> or <code>TABLESWITCH</code>.
     *
     * @param pos       the index at which a byte sequence is inserted.
     * @param code      inserted bytecode sequence.
     * @return          the index indicating the first byte of the
     *                  inserted byte sequence, which might be
     *                  different from pos.
     * @since 3.11
     */
    public int insertAt(int pos, byte[] code) throws BadBytecode {
        return insert0(pos, code, false);
    }

    
Inserts the given bytecode sequence exclusively
before the next instruction that would be returned by
next() (not before the instruction returned
by tha last call to next()).
Branch offsets and the exception table are also updated.

If the next instruction is at the beginning of a block statement,
then the bytecode is excluded from that block.

An extra gap may be inserted at the end of the inserted
bytecode sequence for adjusting alignment if the code attribute
includes LOOKUPSWITCH or TABLESWITCH.

Params:
  • code –      inserted bytecode sequence.
Returns:         the index indicating the first byte of the
                 inserted byte sequence.
/**
     * Inserts the given bytecode sequence exclusively
     * before the next instruction that would be returned by
     * <code>next()</code> (not before the instruction returned
     * by tha last call to <code>next()</code>).
     * Branch offsets and the exception table are also updated.
     *
     * <p>If the next instruction is at the beginning of a block statement,
     * then the bytecode is excluded from that block.
     *
     * <p>An extra gap may be inserted at the end of the inserted
     * bytecode sequence for adjusting alignment if the code attribute
     * includes <code>LOOKUPSWITCH</code> or <code>TABLESWITCH</code>.
     *
     * @param code      inserted bytecode sequence.
     * @return          the index indicating the first byte of the
     *                  inserted byte sequence.
     */
    public int insertEx(byte[] code)
        throws BadBytecode
    {
        return insert0(currentPos, code, true);
    }

    
Inserts the given bytecode sequence exclusively
before the instruction at the given index pos.
Branch offsets and the exception table are also updated.

If the instruction at the given index is at the beginning
of a block statement,
then the bytecode is excluded from that block.

An extra gap may be inserted at the end of the inserted
bytecode sequence for adjusting alignment if the code attribute
includes LOOKUPSWITCH or TABLESWITCH.

The index at which the byte sequence is actually inserted
might be different from pos since some other bytes might be
inserted at other positions (e.g. to change GOTO
to GOTO_W). 

Params:
  • pos –       the index at which a byte sequence is inserted.
  • code –      inserted bytecode sequence.
/**
     * Inserts the given bytecode sequence exclusively
     * before the instruction at the given index <code>pos</code>.
     * Branch offsets and the exception table are also updated.
     *
     * <p>If the instruction at the given index is at the beginning
     * of a block statement,
     * then the bytecode is excluded from that block.
     *
     * <p>An extra gap may be inserted at the end of the inserted
     * bytecode sequence for adjusting alignment if the code attribute
     * includes <code>LOOKUPSWITCH</code> or <code>TABLESWITCH</code>.
     *
     * <p>The index at which the byte sequence is actually inserted
     * might be different from pos since some other bytes might be
     * inserted at other positions (e.g. to change <code>GOTO</code>
     * to <code>GOTO_W</code>). 
     *
     * @param pos       the index at which a byte sequence is inserted.
     * @param code      inserted bytecode sequence.
     */
    public void insertEx(int pos, byte[] code) throws BadBytecode {
        insert0(pos, code, true);
    }

    
Inserts the given bytecode sequence exclusively
before the instruction at the given index pos.
Branch offsets and the exception table are also updated.

If the instruction at the given index is at the beginning
of a block statement,
then the bytecode is excluded from that block.

An extra gap may be inserted at the end of the inserted
bytecode sequence for adjusting alignment if the code attribute
includes LOOKUPSWITCH or TABLESWITCH.

Params:
  • pos –       the index at which a byte sequence is inserted.
  • code –      inserted bytecode sequence.
Returns:         the index indicating the first byte of the
                 inserted byte sequence, which might be
                 different from pos.
Since:3.11
/**
     * Inserts the given bytecode sequence exclusively
     * before the instruction at the given index <code>pos</code>.
     * Branch offsets and the exception table are also updated.
     *
     * <p>If the instruction at the given index is at the beginning
     * of a block statement,
     * then the bytecode is excluded from that block.
     *
     * <p>An extra gap may be inserted at the end of the inserted
     * bytecode sequence for adjusting alignment if the code attribute
     * includes <code>LOOKUPSWITCH</code> or <code>TABLESWITCH</code>.
     *
     * @param pos       the index at which a byte sequence is inserted.
     * @param code      inserted bytecode sequence.
     * @return          the index indicating the first byte of the
     *                  inserted byte sequence, which might be
     *                  different from pos.
     * @since 3.11
     */
    public int insertExAt(int pos, byte[] code) throws BadBytecode {
        return insert0(pos, code, true);
    }

    
Returns:         the index indicating the first byte of the
                 inserted byte sequence.
/**
     * @return          the index indicating the first byte of the
     *                  inserted byte sequence.
     */
    private int insert0(int pos, byte[] code, boolean exclusive)
        throws BadBytecode
    {
        int len = code.length;
        if (len <= 0)
            return pos;

        // currentPos will change.
        pos = insertGapAt(pos, len, exclusive).position;

        int p = pos;
        for (int j = 0; j < len; ++j)
            bytecode[p++] = code[j];

        return pos;
    }

    
Inserts a gap
before the next instruction that would be returned by
next() (not before the instruction returned
by the last call to next()).
Branch offsets and the exception table are also updated.
The inserted gap is filled with NOP.  The gap length may be
extended to a multiple of 4.

If the next instruction is at the beginning of a block statement,
then the gap is inserted within that block.

Params:
  • length –            gap length
Returns: the index indicating the first byte of the inserted gap.
/**
     * Inserts a gap
     * before the next instruction that would be returned by
     * <code>next()</code> (not before the instruction returned
     * by the last call to <code>next()</code>).
     * Branch offsets and the exception table are also updated.
     * The inserted gap is filled with NOP.  The gap length may be
     * extended to a multiple of 4.
     *
     * <p>If the next instruction is at the beginning of a block statement,
     * then the gap is inserted within that block.
     *
     * @param length            gap length
     * @return  the index indicating the first byte of the inserted gap.
     */
    public int insertGap(int length) throws BadBytecode {
        return insertGapAt(currentPos, length, false).position;
    }

    
Inserts a gap in front of the instruction at the given
index pos.
Branch offsets and the exception table are also updated.
The inserted gap is filled with NOP.  The gap length may be
extended to a multiple of 4.

If the instruction at the given index is at the beginning
of a block statement,
then the gap is inserted within that block.

Params:
  • pos –               the index at which a gap is inserted.
  • length –            gap length.
Returns:the length of the inserted gap.
         It might be bigger than length.
/**
     * Inserts a gap in front of the instruction at the given
     * index <code>pos</code>.
     * Branch offsets and the exception table are also updated.
     * The inserted gap is filled with NOP.  The gap length may be
     * extended to a multiple of 4.
     *
     * <p>If the instruction at the given index is at the beginning
     * of a block statement,
     * then the gap is inserted within that block.
     *
     * @param pos               the index at which a gap is inserted.
     * @param length            gap length.
     * @return the length of the inserted gap.
     *          It might be bigger than <code>length</code>.
     */
    public int insertGap(int pos, int length) throws BadBytecode {
        return insertGapAt(pos, length, false).length;
    }

    
Inserts an exclusive gap
before the next instruction that would be returned by
next() (not before the instruction returned
by the last call to next()).
Branch offsets and the exception table are also updated.
The inserted gap is filled with NOP.  The gap length may be
extended to a multiple of 4.

If the next instruction is at the beginning of a block statement,
then the gap is excluded from that block.

Params:
  • length –            gap length
Returns: the index indicating the first byte of the inserted gap.
/**
     * Inserts an exclusive gap
     * before the next instruction that would be returned by
     * <code>next()</code> (not before the instruction returned
     * by the last call to <code>next()</code>).
     * Branch offsets and the exception table are also updated.
     * The inserted gap is filled with NOP.  The gap length may be
     * extended to a multiple of 4.
     *
     * <p>If the next instruction is at the beginning of a block statement,
     * then the gap is excluded from that block.
     *
     * @param length            gap length
     * @return  the index indicating the first byte of the inserted gap.
     */
    public int insertExGap(int length) throws BadBytecode {
        return insertGapAt(currentPos, length, true).position;
    }

    
Inserts an exclusive gap in front of the instruction at the given
index pos.
Branch offsets and the exception table are also updated.
The inserted gap is filled with NOP.  The gap length may be
extended to a multiple of 4.

If the instruction at the given index is at the beginning
of a block statement,
then the gap is excluded from that block.

Params:
  • pos –               the index at which a gap is inserted.
  • length –            gap length.
Returns:the length of the inserted gap.
         It might be bigger than length.
/**
     * Inserts an exclusive gap in front of the instruction at the given
     * index <code>pos</code>.
     * Branch offsets and the exception table are also updated.
     * The inserted gap is filled with NOP.  The gap length may be
     * extended to a multiple of 4.
     *
     * <p>If the instruction at the given index is at the beginning
     * of a block statement,
     * then the gap is excluded from that block.
     *
     * @param pos               the index at which a gap is inserted.
     * @param length            gap length.
     * @return the length of the inserted gap.
     *          It might be bigger than <code>length</code>.
     */
    public int insertExGap(int pos, int length) throws BadBytecode {
        return insertGapAt(pos, length, true).length;
    }

    
An inserted gap.

Since:3.11
/**
     * An inserted gap.
     *
     * @since 3.11
     */
    public static class Gap {
        
The position of the gap.

/**
         * The position of the gap.
         */
        public int position;

        
The length of the gap.

/**
         * The length of the gap.
         */
        public int length;
    }

    
Inserts an inclusive or exclusive gap in front of the instruction
at the given index pos.
Branch offsets and the exception table in the method body
are also updated.  The inserted gap is filled with NOP.
The gap length may be extended to a multiple of 4.

Suppose that the instruction at the given index is at the
beginning of a block statement.  If the gap is inclusive,
then it is included within that block.  If the gap is exclusive,
then it is excluded from that block.

The index at which the gap is actually inserted
might be different from pos since some other bytes might be
inserted at other positions (e.g. to change GOTO
to GOTO_W).  The index is available from the Gap
object returned by this method.

Suppose that the gap is inserted at the position of
the next instruction that would be returned by
next() (not the last instruction returned
by the last call to next()).  The next
instruction returned by next() after the gap is
inserted is still the same instruction.  It is not NOP
at the first byte of the inserted gap.

Params:
  • pos –               the index at which a gap is inserted.
  • length –            gap length.
  • exclusive –         true if exclusive, otherwise false.
Returns:the position and the length of the inserted gap.
Since:3.11
/**
     * Inserts an inclusive or exclusive gap in front of the instruction
     * at the given index <code>pos</code>.
     * Branch offsets and the exception table in the method body
     * are also updated.  The inserted gap is filled with NOP.
     * The gap length may be extended to a multiple of 4.
     *
     * <p>Suppose that the instruction at the given index is at the
     * beginning of a block statement.  If the gap is inclusive,
     * then it is included within that block.  If the gap is exclusive,
     * then it is excluded from that block.
     *
     * <p>The index at which the gap is actually inserted
     * might be different from pos since some other bytes might be
     * inserted at other positions (e.g. to change <code>GOTO</code>
     * to <code>GOTO_W</code>).  The index is available from the <code>Gap</code>
     * object returned by this method.
     *
     * <p>Suppose that the gap is inserted at the position of
     * the next instruction that would be returned by
     * <code>next()</code> (not the last instruction returned
     * by the last call to <code>next()</code>).  The next
     * instruction returned by <code>next()</code> after the gap is
     * inserted is still the same instruction.  It is not <code>NOP</code>
     * at the first byte of the inserted gap.
     *
     * @param pos               the index at which a gap is inserted.
     * @param length            gap length.
     * @param exclusive         true if exclusive, otherwise false.
     * @return the position and the length of the inserted gap.
     * @since 3.11
     */
    public Gap insertGapAt(int pos, int length, boolean exclusive)
        throws BadBytecode
    {
        /**
         * cursorPos indicates the next bytecode whichever exclusive is
         * true or false.
         */
        Gap gap = new Gap();
        if (length <= 0) {
            gap.position = pos;
            gap.length = 0;
            return gap;
        }

        byte[] c;
        int length2;
        if (bytecode.length + length > Short.MAX_VALUE) {
            // currentPos might change after calling insertGapCore0w().
            c = insertGapCore0w(bytecode, pos, length, exclusive,
                                get().getExceptionTable(), codeAttr, gap);
            pos = gap.position;
            length2 = length; // == gap.length
        }
        else {
            int cur = currentPos;
            c = insertGapCore0(bytecode, pos, length, exclusive,
                                      get().getExceptionTable(), codeAttr);
            // insertGapCore0() never changes pos.
            length2 = c.length - bytecode.length;
            gap.position = pos;
            gap.length = length2;
            if (cur >= pos)
                currentPos = cur + length2;

            if (mark > pos || (mark == pos && exclusive))
                mark += length2;

            if (mark2 > pos || (mark2 == pos && exclusive))
                mark2 += length2;
        }

        codeAttr.setCode(c);
        bytecode = c;
        endPos = getCodeLength();
        updateCursors(pos, length2);
        return gap;
    }

    
Is called when a gap is inserted.  The default implementation is empty.
A subclass can override this method so that cursors will be updated.

Params:
  • pos –           the position where a gap is inserted.
  • length –        the length of the gap.
/**
     * Is called when a gap is inserted.  The default implementation is empty.
     * A subclass can override this method so that cursors will be updated.
     *
     * @param pos           the position where a gap is inserted.
     * @param length        the length of the gap.
     */
    protected void updateCursors(int pos, int length) {
        // empty
    }

    
Copies and inserts the entries in the given exception table
at the beginning of the exception table in the code attribute
edited by this object.

Params:
  • offset –    the value added to the code positions included
                         in the entries.
/**
     * Copies and inserts the entries in the given exception table
     * at the beginning of the exception table in the code attribute
     * edited by this object.
     *
     * @param offset    the value added to the code positions included
     *                          in the entries.
     */
    public void insert(ExceptionTable et, int offset) {
        codeAttr.getExceptionTable().add(0, et, offset);
    }

    
Appends the given bytecode sequence at the end.

Params:
  • code –      the bytecode appended.
Returns: the position of the first byte of the appended bytecode.
/**
     * Appends the given bytecode sequence at the end.
     *
     * @param code      the bytecode appended.
     * @return  the position of the first byte of the appended bytecode.
     */
    public int append(byte[] code) {
        int size = getCodeLength();
        int len = code.length;
        if (len <= 0)
            return size;

        appendGap(len);
        byte[] dest = bytecode;
        for (int i = 0; i < len; ++i)
            dest[i + size] = code[i];

        return size;
    }

    
Appends a gap at the end of the bytecode sequence.

Params:
  • gapLength –            gap length
/**
     * Appends a gap at the end of the bytecode sequence.
     *
     * @param gapLength            gap length
     */
    public void appendGap(int gapLength) {
        byte[] code = bytecode;
        int codeLength = code.length;
        byte[] newcode = new byte[codeLength + gapLength];

        int i;
        for (i = 0; i < codeLength; ++i)
            newcode[i] = code[i];

        for (i = codeLength; i < codeLength + gapLength; ++i)
            newcode[i] = NOP;

        codeAttr.setCode(newcode);
        bytecode = newcode;
        endPos = getCodeLength();
    }

    
Copies and appends the entries in the given exception table
at the end of the exception table in the code attribute
edited by this object.

Params:
  • offset –    the value added to the code positions included
                         in the entries.
/**
     * Copies and appends the entries in the given exception table
     * at the end of the exception table in the code attribute
     * edited by this object.
     *
     * @param offset    the value added to the code positions included
     *                          in the entries.
     */
    public void append(ExceptionTable et, int offset) {
        ExceptionTable table = codeAttr.getExceptionTable();
        table.add(table.size(), et, offset);
    }

    /* opcodeLegth is used for implementing nextOpcode().
     */
    private static final int opcodeLength[] = {
        1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 3, 2, 3,
        3, 2, 2, 2, 2, 2, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
        1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 2, 2, 2, 2, 1,
        1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
        1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
        1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
        1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 3, 1, 1, 1, 1, 1, 1, 1,
        1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 3, 3, 3, 3, 3, 3, 3,
        3, 3, 3, 3, 3, 3, 3, 3, 3, 2, 0, 0, 1, 1, 1, 1, 1, 1, 3, 3,
        3, 3, 3, 3, 3, 5, 5, 3, 2, 3, 1, 1, 3, 3, 1, 1, 0, 4, 3, 3,
        5, 5
    };
    // 0 .. LOOKUPSWITCH, TABLESWITCH, WIDE

    
Calculates the index of the next opcode.

/**
     * Calculates the index of the next opcode.
     */
    static int nextOpcode(byte[] code, int index)
        throws BadBytecode
    {
        int opcode;
        try {
            opcode = code[index] & 0xff;
        }
        catch (IndexOutOfBoundsException e) {
            throw new BadBytecode("invalid opcode address");
        }

        try {
            int len = opcodeLength[opcode];
            if (len > 0)
                return index + len;
            else if (opcode == WIDE)
                if (code[index + 1] == (byte)IINC)      // WIDE IINC
                    return index + 6;
                else
                    return index + 4;           // WIDE ...
            int index2 = (index & ~3) + 8;
            if (opcode == LOOKUPSWITCH) {
                int npairs = ByteArray.read32bit(code, index2);
                return index2 + npairs * 8 + 4;
            }
            else if (opcode == TABLESWITCH) {
                int low = ByteArray.read32bit(code, index2);
                int high = ByteArray.read32bit(code, index2 + 4);
                return index2 + (high - low + 1) * 4 + 8;
            }
        }
        catch (IndexOutOfBoundsException e) {
        }

        // opcode is UNUSED or an IndexOutOfBoundsException was thrown.
        throw new BadBytecode(opcode);
    }

    // methods for implementing insertGap().

    static class AlignmentException extends Exception {

        
default serialVersionUID 
/** default serialVersionUID */
        private static final long serialVersionUID = 1L;}

    
insertGapCore0() inserts a gap (some NOPs).
It cannot handle a long code sequence more than 32K.  All branch offsets must be
signed 16bits. 
If "where" is the beginning of a block statement and exclusive is false,
then the inserted gap is also included in the block statement.
"where" must indicate the first byte of an opcode.
The inserted gap is filled with NOP.  gapLength may be extended to
a multiple of 4.
This method was also called from CodeAttribute.LdcEntry.doit().

Params:
  • where –       It must indicate the first byte of an opcode.
/**
     * insertGapCore0() inserts a gap (some NOPs).
     * It cannot handle a long code sequence more than 32K.  All branch offsets must be
     * signed 16bits. 
     *
     * If "where" is the beginning of a block statement and exclusive is false,
     * then the inserted gap is also included in the block statement.
     * "where" must indicate the first byte of an opcode.
     * The inserted gap is filled with NOP.  gapLength may be extended to
     * a multiple of 4.
     *
     * This method was also called from CodeAttribute.LdcEntry.doit().
     *
     * @param where       It must indicate the first byte of an opcode.
     */
    static byte[] insertGapCore0(byte[] code, int where, int gapLength,
                                 boolean exclusive, ExceptionTable etable, CodeAttribute ca)
        throws BadBytecode
    {
        if (gapLength <= 0)
            return code;

        try {
            return insertGapCore1(code, where, gapLength, exclusive, etable, ca);
        }
        catch (AlignmentException e) {
            try {
                return insertGapCore1(code, where, (gapLength + 3) & ~3,
                                  exclusive, etable, ca);
            }
            catch (AlignmentException e2) {
                throw new RuntimeException("fatal error?");
            }
        }
    }

    private static byte[] insertGapCore1(byte[] code, int where, int gapLength,
                                         boolean exclusive, ExceptionTable etable,
                                         CodeAttribute ca)
        throws BadBytecode, AlignmentException
    {
        int codeLength = code.length;
        byte[] newcode = new byte[codeLength + gapLength];
        insertGap2(code, where, gapLength, codeLength, newcode, exclusive);
        etable.shiftPc(where, gapLength, exclusive);
        LineNumberAttribute na
            = (LineNumberAttribute)ca.getAttribute(LineNumberAttribute.tag);
        if (na != null)
            na.shiftPc(where, gapLength, exclusive);

        LocalVariableAttribute va = (LocalVariableAttribute)ca.getAttribute(
                                                LocalVariableAttribute.tag);
        if (va != null)
            va.shiftPc(where, gapLength, exclusive);

        LocalVariableAttribute vta
            = (LocalVariableAttribute)ca.getAttribute(
                                              LocalVariableAttribute.typeTag);
        if (vta != null)
            vta.shiftPc(where, gapLength, exclusive);

        StackMapTable smt = (StackMapTable)ca.getAttribute(StackMapTable.tag);
        if (smt != null)
            smt.shiftPc(where, gapLength, exclusive);

        StackMap sm = (StackMap)ca.getAttribute(StackMap.tag);
        if (sm != null)
            sm.shiftPc(where, gapLength, exclusive);

        return newcode;
    }

    private static void insertGap2(byte[] code, int where, int gapLength,
                        int endPos, byte[] newcode, boolean exclusive)
        throws BadBytecode, AlignmentException
    {
        int nextPos;
        int i = 0;
        int j = 0;
        for (; i < endPos; i = nextPos) {
            if (i == where) {
                int j2 = j + gapLength;
                while (j < j2)
                    newcode[j++] = NOP;
            }

            nextPos = nextOpcode(code, i);
            int inst = code[i] & 0xff;
            // if<cond>, if_icmp<cond>, if_acmp<cond>, goto, jsr
            if ((153 <= inst && inst <= 168)
                || inst == IFNULL || inst == IFNONNULL) {
                /* 2bytes *signed* offset */
                int offset = (code[i + 1] << 8) | (code[i + 2] & 0xff);
                offset = newOffset(i, offset, where, gapLength, exclusive);
                newcode[j] = code[i];
                ByteArray.write16bit(offset, newcode, j + 1);
                j += 3;
            }
            else if (inst == GOTO_W || inst == JSR_W) {
                /* 4bytes offset */
                int offset = ByteArray.read32bit(code, i + 1);
                offset = newOffset(i, offset, where, gapLength, exclusive);
                newcode[j++] = code[i];
                ByteArray.write32bit(offset, newcode, j);
                j += 4;
            }
            else if (inst == TABLESWITCH) {
                if (i != j && (gapLength & 3) != 0)
                    throw new AlignmentException();

                int i2 = (i & ~3) + 4;  // 0-3 byte padding
                // IBM JVM 1.4.2 cannot run the following code:
                // int i0 = i;
                // while (i0 < i2)
                //    newcode[j++] = code[i0++];
                // So extracting this code into an external method.
                // see JIRA JASSIST-74.
                j = copyGapBytes(newcode, j, code, i, i2);

                int defaultbyte = newOffset(i, ByteArray.read32bit(code, i2),
                                            where, gapLength, exclusive);
                ByteArray.write32bit(defaultbyte, newcode, j);
                int lowbyte = ByteArray.read32bit(code, i2 + 4);
                ByteArray.write32bit(lowbyte, newcode, j + 4);
                int highbyte = ByteArray.read32bit(code, i2 + 8);
                ByteArray.write32bit(highbyte, newcode, j + 8);
                j += 12;
                int i0 = i2 + 12;
                i2 = i0 + (highbyte - lowbyte + 1) * 4;
                while (i0 < i2) {
                    int offset = newOffset(i, ByteArray.read32bit(code, i0),
                                           where, gapLength, exclusive);
                    ByteArray.write32bit(offset, newcode, j);
                    j += 4;
                    i0 += 4;
                }
            }
            else if (inst == LOOKUPSWITCH) {
                if (i != j && (gapLength & 3) != 0)
                    throw new AlignmentException();

                int i2 = (i & ~3) + 4;  // 0-3 byte padding

                // IBM JVM 1.4.2 cannot run the following code:
                // int i0 = i;
                // while (i0 < i2)
                //    newcode[j++] = code[i0++];
                // So extracting this code into an external method.
                // see JIRA JASSIST-74.
                j = copyGapBytes(newcode, j, code, i, i2);

                int defaultbyte = newOffset(i, ByteArray.read32bit(code, i2),
                                            where, gapLength, exclusive);
                ByteArray.write32bit(defaultbyte, newcode, j);
                int npairs = ByteArray.read32bit(code, i2 + 4);
                ByteArray.write32bit(npairs, newcode, j + 4);
                j += 8;
                int i0 = i2 + 8;
                i2 = i0 + npairs * 8;
                while (i0 < i2) {
                    ByteArray.copy32bit(code, i0, newcode, j);
                    int offset = newOffset(i,
                                        ByteArray.read32bit(code, i0 + 4),
                                        where, gapLength, exclusive);
                    ByteArray.write32bit(offset, newcode, j + 4);
                    j += 8;
                    i0 += 8;
                }
            }
            else
                while (i < nextPos)
                    newcode[j++] = code[i++];
            }
    }


    private static int copyGapBytes(byte[] newcode, int j, byte[] code, int i, int iEnd) {
        switch (iEnd - i) {
        case 4:
            newcode[j++] = code[i++];
        case 3:
            newcode[j++] = code[i++];
        case 2:
            newcode[j++] = code[i++];
        case 1:
            newcode[j++] = code[i++];
        default:
        }

        return j;
    }

    private static int newOffset(int i, int offset, int where,
                                 int gapLength, boolean exclusive) {
        int target = i + offset;
        if (i < where) {
            if (where < target || (exclusive && where == target))
                offset += gapLength;
        }
        else if (i == where) {
            // This code is different from the code in Branch#shiftOffset().
            // see JASSIST-124.
            if (target < where)
                offset -= gapLength;
        }
        else
            if (target < where || (!exclusive && where == target))
                offset -= gapLength;

        return offset;
    }

    static class Pointers {
        int cursor;
        int mark0, mark, mark2;
        ExceptionTable etable;
        LineNumberAttribute line;
        LocalVariableAttribute vars, types;
        StackMapTable stack;
        StackMap stack2;

        Pointers(int cur, int m, int m2, int m0, ExceptionTable et, CodeAttribute ca) {
            cursor = cur;
            mark = m;
            mark2 = m2;
            mark0 = m0;
            etable = et;    // non null
            line = (LineNumberAttribute)ca.getAttribute(LineNumberAttribute.tag);
            vars = (LocalVariableAttribute)ca.getAttribute(LocalVariableAttribute.tag);
            types = (LocalVariableAttribute)ca.getAttribute(LocalVariableAttribute.typeTag);
            stack = (StackMapTable)ca.getAttribute(StackMapTable.tag);
            stack2 = (StackMap)ca.getAttribute(StackMap.tag);
        }

        void shiftPc(int where, int gapLength, boolean exclusive) throws BadBytecode {
            if (where < cursor || (where == cursor && exclusive))
                cursor += gapLength;

            if (where < mark || (where == mark && exclusive))
                mark += gapLength;

            if (where < mark2 || (where == mark2 && exclusive))
                mark2 += gapLength;

            if (where < mark0 || (where == mark0 && exclusive))
                mark0 += gapLength;

            etable.shiftPc(where, gapLength, exclusive);
            if (line != null)
                line.shiftPc(where, gapLength, exclusive);

            if (vars != null)
                vars.shiftPc(where, gapLength, exclusive);

            if (types != null)
                types.shiftPc(where, gapLength, exclusive);

            if (stack != null)
                stack.shiftPc(where, gapLength, exclusive);

            if (stack2 != null)
                stack2.shiftPc(where, gapLength, exclusive);
        }

        void shiftForSwitch(int where, int gapLength) throws BadBytecode {
            if (stack != null)
                stack.shiftForSwitch(where, gapLength);

            if (stack2 != null)
                stack2.shiftForSwitch(where, gapLength);
        }
    }

    /*
     * This method is called from CodeAttribute.LdcEntry.doit().
     */
    static byte[] changeLdcToLdcW(byte[] code, ExceptionTable etable,
                                  CodeAttribute ca, CodeAttribute.LdcEntry ldcs)
        throws BadBytecode
    {
        Pointers pointers = new Pointers(0, 0, 0, 0, etable, ca);
        List<Branch> jumps = makeJumpList(code, code.length, pointers);
        while (ldcs != null) {
            addLdcW(ldcs, jumps);
            ldcs = ldcs.next;
        }

        byte[] r = insertGap2w(code, 0, 0, false, jumps, pointers);
        return r;
    }

    private static void addLdcW(CodeAttribute.LdcEntry ldcs, List<Branch> jumps) {
        int where = ldcs.where;
        LdcW ldcw = new LdcW(where, ldcs.index);
        int s = jumps.size();
        for (int i = 0; i < s; i++)
            if (where < jumps.get(i).orgPos) {
                jumps.add(i, ldcw);
                return;
            }

        jumps.add(ldcw);
    }

    /*
     * insertGapCore0w() can handle a long code sequence more than 32K. 
     * It guarantees that the length of the inserted gap (NOPs) is equal to
     * gapLength.  No other NOPs except some NOPs following TABLESWITCH or
     * LOOKUPSWITCH will not be inserted. 
     * 
     * Note: currentPos might be moved.
     *
     * @param where       It must indicate the first byte of an opcode.
     * @param newWhere    It contains the updated index of the position where a gap
     *                    is inserted and the length of the gap.
     *                    It must not be null.
     */
    private byte[] insertGapCore0w(byte[] code, int where, int gapLength, boolean exclusive,
                                   ExceptionTable etable, CodeAttribute ca, Gap newWhere)
        throws BadBytecode
    {
        if (gapLength <= 0)
            return code;

        Pointers pointers = new Pointers(currentPos, mark, mark2, where, etable, ca);
        List<Branch> jumps = makeJumpList(code, code.length, pointers);
        byte[] r = insertGap2w(code, where, gapLength, exclusive, jumps, pointers);
        currentPos = pointers.cursor;
        mark = pointers.mark;
        mark2 = pointers.mark2;
        int where2 = pointers.mark0;
        if (where2 == currentPos && !exclusive)
            currentPos += gapLength;

        if (exclusive)
            where2 -= gapLength;

        newWhere.position = where2;
        newWhere.length = gapLength;
        return r;
    }

    private static byte[] insertGap2w(byte[] code, int where, int gapLength,
                                      boolean exclusive, List<Branch> jumps, Pointers ptrs)
        throws BadBytecode
    {
        if (gapLength > 0) {
            ptrs.shiftPc(where, gapLength, exclusive);
            for (Branch b:jumps)
                b.shift(where, gapLength, exclusive);
        }

        boolean unstable = true;
        do {
            while (unstable) {
                unstable = false;
                for (Branch b:jumps) {
                    if (b.expanded()) {
                        unstable = true;
                        int p = b.pos;
                        int delta = b.deltaSize();
                        ptrs.shiftPc(p, delta, false);
                        for (Branch bb:jumps)
                            bb.shift(p, delta, false);
                    }
                }
            }

            for (Branch b:jumps) {
                int diff = b.gapChanged();
                if (diff > 0) {
                    unstable = true;
                    int p = b.pos;
                    ptrs.shiftPc(p, diff, false);
                    for (Branch bb:jumps)
                        bb.shift(p, diff, false);
                }
            }
        } while (unstable);

        return makeExapndedCode(code, jumps, where, gapLength);
    }

    private static List<Branch> makeJumpList(byte[] code, int endPos, Pointers ptrs)
        throws BadBytecode
    {
        List<Branch> jumps = new ArrayList<Branch>();
        int nextPos;
        for (int i = 0; i < endPos; i = nextPos) {
            nextPos = nextOpcode(code, i);
            int inst = code[i] & 0xff;
            // if<cond>, if_icmp<cond>, if_acmp<cond>, goto, jsr
            if ((153 <= inst && inst <= 168)
                    || inst == IFNULL || inst == IFNONNULL) {
                /* 2bytes *signed* offset */
                int offset = (code[i + 1] << 8) | (code[i + 2] & 0xff);
                Branch b;
                if (inst == GOTO || inst == JSR)
                    b = new Jump16(i, offset);
                else
                    b = new If16(i, offset);

                jumps.add(b);
            }
            else if (inst == GOTO_W || inst == JSR_W) {
                /* 4bytes offset */
                int offset = ByteArray.read32bit(code, i + 1);
                jumps.add(new Jump32(i, offset));
            }
            else if (inst == TABLESWITCH) {
                int i2 = (i & ~3) + 4;  // 0-3 byte padding
                int defaultbyte = ByteArray.read32bit(code, i2);
                int lowbyte = ByteArray.read32bit(code, i2 + 4);
                int highbyte = ByteArray.read32bit(code, i2 + 8);
                int i0 = i2 + 12;
                int size = highbyte - lowbyte + 1;
                int[] offsets = new int[size];
                for (int j = 0; j < size; j++) {
                    offsets[j] = ByteArray.read32bit(code, i0);
                    i0 += 4;
                }

                jumps.add(new Table(i, defaultbyte, lowbyte, highbyte, offsets, ptrs));
            }
            else if (inst == LOOKUPSWITCH) {
                int i2 = (i & ~3) + 4;  // 0-3 byte padding
                int defaultbyte = ByteArray.read32bit(code, i2);
                int npairs = ByteArray.read32bit(code, i2 + 4);
                int i0 = i2 + 8;
                int[] matches = new int[npairs];
                int[] offsets = new int[npairs];
                for (int j = 0; j < npairs; j++) {
                    matches[j] = ByteArray.read32bit(code, i0);
                    offsets[j] = ByteArray.read32bit(code, i0 + 4);
                    i0 += 8;
                }

                jumps.add(new Lookup(i, defaultbyte, matches, offsets, ptrs));
            }
        }

        return jumps;
    }

    private static byte[] makeExapndedCode(byte[] code, List<Branch> jumps,
                                           int where, int gapLength)
        throws BadBytecode
    {
        int n = jumps.size();
        int size = code.length + gapLength;
        for (Branch b:jumps)
            size += b.deltaSize();

        byte[] newcode = new byte[size];
        int src = 0, dest = 0, bindex = 0;
        int len = code.length;
        Branch b;
        int bpos;
        if (0 < n) {
            b = jumps.get(0);
            bpos = b.orgPos;
        }
        else {
            b = null;
            bpos = len;  // src will be never equal to bpos
        }

        while (src < len) {
            if (src == where) {
                int pos2 = dest + gapLength;
                while (dest < pos2)
                    newcode[dest++] = NOP;
            }

            if (src != bpos)
                newcode[dest++] = code[src++];
            else {
                int s = b.write(src, code, dest, newcode);
                src += s;
                dest += s + b.deltaSize();
                if (++bindex < n) {
                    b = jumps.get(bindex);
                    bpos = b.orgPos;
                }
                else  {
                    b = null;
                    bpos = len;
                }
            }
        }

        return newcode;
    }

    static abstract class Branch {
        int pos, orgPos;
        Branch(int p) { pos = orgPos = p; }
        void shift(int where, int gapLength, boolean exclusive) {
            if (where < pos || (where == pos && exclusive))
                pos += gapLength;
        }

        static int shiftOffset(int i, int offset, int where,
                               int gapLength, boolean exclusive) {
            int target = i + offset;
            if (i < where) {
                if (where < target || (exclusive && where == target))
                    offset += gapLength;
            }
            else if (i == where) {
                // This code is different from the code in CodeIterator#newOffset().
                // see JASSIST-124.
                if (target < where && exclusive)
                    offset -= gapLength;
                else if (where < target && !exclusive)
                    offset += gapLength;
            }
            else
                if (target < where || (!exclusive && where == target))
                    offset -= gapLength;

            return offset;
        }

        boolean expanded() { return false; }
        int gapChanged() { return 0; }
        int deltaSize() { return 0; }   // newSize - oldSize

        // This returns the original instruction size.
        abstract int write(int srcPos, byte[] code, int destPos, byte[] newcode) throws BadBytecode;
    }

    /* used by changeLdcToLdcW() and CodeAttribute.LdcEntry.
     */
    static class LdcW extends Branch {
        int index;
        boolean state;
        LdcW(int p, int i) {
            super(p);
            index = i;
            state = true;
        }

        @Override
        boolean expanded() {
            if (state) {
                state = false;
                return true;
            }
            return false;
        }

        @Override
        int deltaSize() { return 1; }

        @Override
        int write(int srcPos, byte[] code, int destPos, byte[] newcode) {
            newcode[destPos] = LDC_W;
            ByteArray.write16bit(index, newcode, destPos + 1);
            return 2;
        }
    }

    static abstract class Branch16 extends Branch {
        int offset;
        int state;
        static final int BIT16 = 0;
        static final int EXPAND = 1;
        static final int BIT32 = 2;

        Branch16(int p, int off) {
            super(p);
            offset = off;
            state = BIT16;
        }

        @Override
        void shift(int where, int gapLength, boolean exclusive) {
            offset = shiftOffset(pos, offset, where, gapLength, exclusive);
            super.shift(where, gapLength, exclusive);
            if (state == BIT16)
                if (offset < Short.MIN_VALUE || Short.MAX_VALUE < offset)
                    state = EXPAND;
        }

        @Override
        boolean expanded() {
            if (state == EXPAND) {
                state = BIT32;
                return true;
            }
            return false;
        }

        @Override
        abstract int deltaSize();
        abstract void write32(int src, byte[] code, int dest, byte[] newcode);

        @Override
        int write(int src, byte[] code, int dest, byte[] newcode) {
            if (state == BIT32)
                write32(src, code, dest, newcode);
            else {
                newcode[dest] = code[src];
                ByteArray.write16bit(offset, newcode, dest + 1);
            }

            return 3;
        }
    }

    // GOTO or JSR
    static class Jump16 extends Branch16 {
        Jump16(int p, int off) {
            super(p, off);
        }

        @Override
        int deltaSize() {
            return state == BIT32 ? 2 : 0;
        }

        @Override
        void write32(int src, byte[] code, int dest, byte[] newcode) {
            newcode[dest] = (byte)(((code[src] & 0xff) == GOTO) ? GOTO_W : JSR_W);
            ByteArray.write32bit(offset, newcode, dest + 1);
        }
    }

    // if<cond>, if_icmp<cond>, or if_acmp<cond>
    static class If16 extends Branch16 {
        If16(int p, int off) {
            super(p, off);
        }

        @Override
        int deltaSize() {
            return state == BIT32 ? 5 : 0;
        }

        @Override
        void write32(int src, byte[] code, int dest, byte[] newcode) {
            newcode[dest] = (byte)opcode(code[src] & 0xff);
            newcode[dest + 1] = 0;
            newcode[dest + 2] = 8;  // branch_offset = 8
            newcode[dest + 3] = (byte)GOTO_W;
            ByteArray.write32bit(offset - 3, newcode, dest + 4);
        }

        int opcode(int op) {
            if (op == IFNULL)
                return IFNONNULL;
            else if (op == IFNONNULL)
                return IFNULL;
            if (((op - IFEQ) & 1) == 0)
                return op + 1;
            return op - 1;
        }
    }

    static class Jump32 extends Branch {
        int offset;

        Jump32(int p, int off) {
            super(p);
            offset = off;
        }

        @Override
        void shift(int where, int gapLength, boolean exclusive) {
            offset = shiftOffset(pos, offset, where, gapLength, exclusive);
            super.shift(where, gapLength, exclusive);
        }

        @Override
        int write(int src, byte[] code, int dest, byte[] newcode) {
            newcode[dest] = code[src];
            ByteArray.write32bit(offset, newcode, dest + 1);
            return 5;
        }
    }

    static abstract class Switcher extends Branch {
        int gap, defaultByte;
        int[] offsets;
        Pointers pointers;

        Switcher(int pos, int defaultByte, int[] offsets, Pointers ptrs) {
            super(pos);
            this.gap = 3 - (pos & 3);
            this.defaultByte = defaultByte;
            this.offsets = offsets;
            this.pointers = ptrs;
        }

        @Override
        void shift(int where, int gapLength, boolean exclusive) {
            int p = pos;
            defaultByte = shiftOffset(p, defaultByte, where, gapLength, exclusive);
            int num = offsets.length;
            for (int i = 0; i < num; i++)
                offsets[i] = shiftOffset(p, offsets[i], where, gapLength, exclusive);

            super.shift(where, gapLength, exclusive);
        }

        @Override
        int gapChanged() {
            int newGap = 3 - (pos & 3);
            if (newGap > gap) {
                int diff = newGap - gap;
                gap = newGap;
                return diff;
            }

            return 0;
        }

        @Override
        int deltaSize() {
            return gap - (3 - (orgPos & 3));
        }

        @Override
        int write(int src, byte[] code, int dest, byte[] newcode) throws BadBytecode {
            int padding = 3 - (pos & 3);
            int nops = gap - padding;
            int bytecodeSize = 5 + (3 - (orgPos & 3)) + tableSize();
            if (nops > 0)
                adjustOffsets(bytecodeSize, nops);

            newcode[dest++] = code[src];
            while (padding-- > 0)
                newcode[dest++] = 0;

            ByteArray.write32bit(defaultByte, newcode, dest);
            int size = write2(dest + 4, newcode);
            dest += size + 4;
            while (nops-- > 0)
                newcode[dest++] = NOP;

            return 5 + (3 - (orgPos & 3)) + size;
        }

        abstract int write2(int dest, byte[] newcode);
        abstract int tableSize();

        /* If the new bytecode size is shorter than the original, some NOPs
         * are appended after this branch instruction (tableswitch or
         * lookupswitch) to fill the gap.
         * This method changes a branch offset to point to the first NOP
         * if the offset originally points to the bytecode next to this
         * branch instruction.  Otherwise, the bytecode would contain
         * dead code.  It complicates the generation of StackMap and
         * StackMapTable.
         */
        void adjustOffsets(int size, int nops) throws BadBytecode {
            pointers.shiftForSwitch(pos + size, nops);
            if (defaultByte == size)
                defaultByte -= nops;

            for (int i = 0; i < offsets.length; i++)
                if (offsets[i] == size)
                    offsets[i] -= nops;
        }
    }

    static class Table extends Switcher {
        int low, high;

        Table(int pos, int defaultByte, int low, int high, int[] offsets, Pointers ptrs) {
            super(pos, defaultByte, offsets, ptrs);
            this.low = low;
            this.high = high;
        }

        @Override
        int write2(int dest, byte[] newcode) {
            ByteArray.write32bit(low, newcode, dest);
            ByteArray.write32bit(high, newcode, dest + 4);
            int n = offsets.length;
            dest += 8;
            for (int i = 0; i < n; i++) {
                ByteArray.write32bit(offsets[i], newcode, dest);
                dest += 4;
            }

            return 8 + 4 * n;
        }

        @Override
        int tableSize() { return 8 + 4 * offsets.length; }
    }

    static class Lookup extends Switcher {
        int[] matches;

        Lookup(int pos, int defaultByte, int[] matches, int[] offsets, Pointers ptrs) {
            super(pos, defaultByte, offsets, ptrs);
            this.matches = matches;
        }

        @Override
        int write2(int dest, byte[] newcode) {
            int n = matches.length;
            ByteArray.write32bit(n, newcode, dest);
            dest += 4;
            for (int i = 0; i < n; i++) {
                ByteArray.write32bit(matches[i], newcode, dest);
                ByteArray.write32bit(offsets[i], newcode, dest + 4);
                dest += 8;
            }

            return 4 + 8 * n;
        }

        @Override
        int tableSize() { return 4 + 8 * matches.length; }
    }
}