/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.commons.lang3.builder;

import java.lang.reflect.AccessibleObject;
import java.lang.reflect.Field;
import java.lang.reflect.Modifier;
import java.util.Arrays;
import java.util.Collection;
import java.util.Comparator;
import java.util.HashSet;
import java.util.Set;

import org.apache.commons.lang3.ArrayUtils;
import org.apache.commons.lang3.Validate;

 Assists in implementing Object.hashCode() methods. 
 This class enables a good hashCode method to be built for any class. It follows the rules laid out in the book Effective Java by Joshua Bloch. Writing a good hashCode method is actually quite difficult. This class aims to simplify the process. 

The following is the approach taken. When appending a data field, the current total is multiplied by the
multiplier then a relevant value
for that data type is added. For example, if the current hashCode is 17, and the multiplier is 37, then
appending the integer 45 will create a hash code of 674, namely 17 * 37 + 45.

 All relevant fields from the object should be included in the hashCode method. Derived fields may be excluded. In general, any field used in the equals method must be used in the hashCode method. 

To use this class write code as follows:

public class Person {
  String name;
  int age;
  boolean smoker;
  ...
  public int hashCode() {
    // you pick a hard-coded, randomly chosen, non-zero, odd number
    // ideally different for each class
    return new HashCodeBuilder(17, 37).
      append(name).
      append(age).
      append(smoker).
      toHashCode();
  }
}

 If required, the superclass hashCode() can be added using appendSuper. 
 Alternatively, there is a method that uses reflection to determine the fields to test. Because these fields are usually private, the method, reflectionHashCode, uses AccessibleObject.setAccessible to change the visibility of the fields. This will fail under a security manager, unless the appropriate permissions are set up correctly. It is also slower than testing explicitly. 

A typical invocation for this method would look like:

public int hashCode() {
  return HashCodeBuilder.reflectionHashCode(this);
}

The HashCodeExclude annotation can be used to exclude fields from being used by the reflectionHashCode methods.
Since:
1.0/**
 * <p>
 * Assists in implementing {@link Object#hashCode()} methods.
 * </p>
 *
 * <p>
 * This class enables a good {@code hashCode} method to be built for any class. It follows the rules laid out in
 * the book <a href="http://www.oracle.com/technetwork/java/effectivejava-136174.html">Effective Java</a> by Joshua Bloch. Writing a
 * good {@code hashCode} method is actually quite difficult. This class aims to simplify the process.
 * </p>
 *
 * <p>
 * The following is the approach taken. When appending a data field, the current total is multiplied by the
 * multiplier then a relevant value
 * for that data type is added. For example, if the current hashCode is 17, and the multiplier is 37, then
 * appending the integer 45 will create a hash code of 674, namely 17 * 37 + 45.
 * </p>
 *
 * <p>
 * All relevant fields from the object should be included in the {@code hashCode} method. Derived fields may be
 * excluded. In general, any field used in the {@code equals} method must be used in the {@code hashCode}
 * method.
 * </p>
 *
 * <p>
 * To use this class write code as follows:
 * </p>
 *
 * <pre>
 * public class Person {
 *   String name;
 *   int age;
 *   boolean smoker;
 *   ...
 *
 *   public int hashCode() {
 *     // you pick a hard-coded, randomly chosen, non-zero, odd number
 *     // ideally different for each class
 *     return new HashCodeBuilder(17, 37).
 *       append(name).
 *       append(age).
 *       append(smoker).
 *       toHashCode();
 *   }
 * }
 * </pre>
 *
 * <p>
 * If required, the superclass {@code hashCode()} can be added using {@link #appendSuper}.
 * </p>
 *
 * <p>
 * Alternatively, there is a method that uses reflection to determine the fields to test. Because these fields are
 * usually private, the method, {@code reflectionHashCode}, uses {@code AccessibleObject.setAccessible}
 * to change the visibility of the fields. This will fail under a security manager, unless the appropriate permissions
 * are set up correctly. It is also slower than testing explicitly.
 * </p>
 *
 * <p>
 * A typical invocation for this method would look like:
 * </p>
 *
 * <pre>
 * public int hashCode() {
 *   return HashCodeBuilder.reflectionHashCode(this);
 * }
 * </pre>
 *
 * <p>The {@link HashCodeExclude} annotation can be used to exclude fields from being
 * used by the {@code reflectionHashCode} methods.</p>
 *
 * @since 1.0
 */
public class HashCodeBuilder implements Builder<Integer> {
    
The default initial value to use in reflection hash code building.
/**
     * The default initial value to use in reflection hash code building.
     */
    private static final int DEFAULT_INITIAL_VALUE = 17;

    
The default multiplier value to use in reflection hash code building.
/**
     * The default multiplier value to use in reflection hash code building.
     */
    private static final int DEFAULT_MULTIPLIER_VALUE = 37;

    

A registry of objects used by reflection methods to detect cyclical object references and avoid infinite loops.

Since:
2.3/**
     * <p>
     * A registry of objects used by reflection methods to detect cyclical object references and avoid infinite loops.
     * </p>
     *
     * @since 2.3
     */
    private static final ThreadLocal<Set<IDKey>> REGISTRY = new ThreadLocal<>();

    /*
     * NOTE: we cannot store the actual objects in a HashSet, as that would use the very hashCode()
     * we are in the process of calculating.
     *
     * So we generate a one-to-one mapping from the original object to a new object.
     *
     * Now HashSet uses equals() to determine if two elements with the same hash code really
     * are equal, so we also need to ensure that the replacement objects are only equal
     * if the original objects are identical.
     *
     * The original implementation (2.4 and before) used the System.identityHashCode()
     * method - however this is not guaranteed to generate unique ids (e.g. LANG-459)
     *
     * We now use the IDKey helper class (adapted from org.apache.axis.utils.IDKey)
     * to disambiguate the duplicate ids.
     */

    

Returns the registry of objects being traversed by the reflection methods in the current thread.

Returns:
Set the registry of objects being traversed
Since:
2.3/**
     * <p>
     * Returns the registry of objects being traversed by the reflection methods in the current thread.
     * </p>
     *
     * @return Set the registry of objects being traversed
     * @since 2.3
     */
    static Set<IDKey> getRegistry() {
        return REGISTRY.get();
    }

    
 Returns true if the registry contains the given object. Used by the reflection methods to avoid infinite loops. 
Params:
value – 
           The object to lookup in the registry.
Returns:
boolean true if the registry contains the given object.
Since:
2.3/**
     * <p>
     * Returns {@code true} if the registry contains the given object. Used by the reflection methods to avoid
     * infinite loops.
     * </p>
     *
     * @param value
     *            The object to lookup in the registry.
     * @return boolean {@code true} if the registry contains the given object.
     * @since 2.3
     */
    static boolean isRegistered(final Object value) {
        final Set<IDKey> registry = getRegistry();
        return registry != null && registry.contains(new IDKey(value));
    }

    
 Appends the fields and values defined by the given object of the given Class. 
Params:
object – 
           the object to append details of
clazz – 
           the class to append details of
builder – 
           the builder to append to
useTransients – 
           whether to use transient fields
excludeFields – 
           Collection of String field names to exclude from use in calculation of hash code/**
     * <p>
     * Appends the fields and values defined by the given object of the given {@code Class}.
     * </p>
     *
     * @param object
     *            the object to append details of
     * @param clazz
     *            the class to append details of
     * @param builder
     *            the builder to append to
     * @param useTransients
     *            whether to use transient fields
     * @param excludeFields
     *            Collection of String field names to exclude from use in calculation of hash code
     */
    private static void reflectionAppend(final Object object, final Class<?> clazz, final HashCodeBuilder builder, final boolean useTransients,
            final String[] excludeFields) {
        if (isRegistered(object)) {
            return;
        }
        try {
            register(object);
            // The elements in the returned array are not sorted and are not in any particular order.
            final Field[] fields = clazz.getDeclaredFields();
            Arrays.sort(fields, Comparator.comparing(Field::getName));
            AccessibleObject.setAccessible(fields, true);
            for (final Field field : fields) {
                if (!ArrayUtils.contains(excludeFields, field.getName())
                    && !field.getName().contains("$")
                    && (useTransients || !Modifier.isTransient(field.getModifiers()))
                    && !Modifier.isStatic(field.getModifiers())
                    && !field.isAnnotationPresent(HashCodeExclude.class)) {
                    try {
                        final Object fieldValue = field.get(object);
                        builder.append(fieldValue);
                    } catch (final IllegalAccessException e) {
                        // this can't happen. Would get a Security exception instead
                        // throw a runtime exception in case the impossible happens.
                        throw new InternalError("Unexpected IllegalAccessException");
                    }
                }
            }
        } finally {
            unregister(object);
        }
    }

    
 Uses reflection to build a valid hash code from the fields of object. 
 It uses AccessibleObject.setAccessible to gain access to private fields. This means that it will throw a security exception if run under a security manager, if the permissions are not set up correctly. It is also not as efficient as testing explicitly. 
 Transient members will be not be used, as they are likely derived fields, and not part of the value of the Object. 

Static fields will not be tested. Superclass fields will be included.


Two randomly chosen, non-zero, odd numbers must be passed in. Ideally these should be different for each class,
however this is not vital. Prime numbers are preferred, especially for the multiplier.

Params:
initialNonZeroOddNumber – 
           a non-zero, odd number used as the initial value. This will be the returned
           value if no fields are found to include in the hash code
multiplierNonZeroOddNumber – 
           a non-zero, odd number used as the multiplier
object –  the Object to create a hashCode for
Throws:
IllegalArgumentException –  if the Object is null
IllegalArgumentException – 
            if the number is zero or even
See Also:
HashCodeExclude
Returns:
int hash code/**
     * <p>
     * Uses reflection to build a valid hash code from the fields of {@code object}.
     * </p>
     *
     * <p>
     * It uses {@code AccessibleObject.setAccessible} to gain access to private fields. This means that it will
     * throw a security exception if run under a security manager, if the permissions are not set up correctly. It is
     * also not as efficient as testing explicitly.
     * </p>
     *
     * <p>
     * Transient members will be not be used, as they are likely derived fields, and not part of the value of the
     * {@code Object}.
     * </p>
     *
     * <p>
     * Static fields will not be tested. Superclass fields will be included.
     * </p>
     *
     * <p>
     * Two randomly chosen, non-zero, odd numbers must be passed in. Ideally these should be different for each class,
     * however this is not vital. Prime numbers are preferred, especially for the multiplier.
     * </p>
     *
     * @param initialNonZeroOddNumber
     *            a non-zero, odd number used as the initial value. This will be the returned
     *            value if no fields are found to include in the hash code
     * @param multiplierNonZeroOddNumber
     *            a non-zero, odd number used as the multiplier
     * @param object
     *            the Object to create a {@code hashCode} for
     * @return int hash code
     * @throws IllegalArgumentException
     *             if the Object is {@code null}
     * @throws IllegalArgumentException
     *             if the number is zero or even
     *
     * @see HashCodeExclude
     */
    public static int reflectionHashCode(final int initialNonZeroOddNumber, final int multiplierNonZeroOddNumber, final Object object) {
        return reflectionHashCode(initialNonZeroOddNumber, multiplierNonZeroOddNumber, object, false, null);
    }

    
 Uses reflection to build a valid hash code from the fields of object. 
 It uses AccessibleObject.setAccessible to gain access to private fields. This means that it will throw a security exception if run under a security manager, if the permissions are not set up correctly. It is also not as efficient as testing explicitly. 
 If the TestTransients parameter is set to true, transient members will be tested, otherwise they are ignored, as they are likely derived fields, and not part of the value of the Object. 

Static fields will not be tested. Superclass fields will be included.


Two randomly chosen, non-zero, odd numbers must be passed in. Ideally these should be different for each class,
however this is not vital. Prime numbers are preferred, especially for the multiplier.

Params:
initialNonZeroOddNumber – 
           a non-zero, odd number used as the initial value. This will be the returned
           value if no fields are found to include in the hash code
multiplierNonZeroOddNumber – 
           a non-zero, odd number used as the multiplier
object –  the Object to create a hashCode for
testTransients – 
           whether to include transient fields
Throws:
IllegalArgumentException –  if the Object is null
IllegalArgumentException – 
            if the number is zero or even
See Also:
HashCodeExclude
Returns:
int hash code/**
     * <p>
     * Uses reflection to build a valid hash code from the fields of {@code object}.
     * </p>
     *
     * <p>
     * It uses {@code AccessibleObject.setAccessible} to gain access to private fields. This means that it will
     * throw a security exception if run under a security manager, if the permissions are not set up correctly. It is
     * also not as efficient as testing explicitly.
     * </p>
     *
     * <p>
     * If the TestTransients parameter is set to {@code true}, transient members will be tested, otherwise they
     * are ignored, as they are likely derived fields, and not part of the value of the {@code Object}.
     * </p>
     *
     * <p>
     * Static fields will not be tested. Superclass fields will be included.
     * </p>
     *
     * <p>
     * Two randomly chosen, non-zero, odd numbers must be passed in. Ideally these should be different for each class,
     * however this is not vital. Prime numbers are preferred, especially for the multiplier.
     * </p>
     *
     * @param initialNonZeroOddNumber
     *            a non-zero, odd number used as the initial value. This will be the returned
     *            value if no fields are found to include in the hash code
     * @param multiplierNonZeroOddNumber
     *            a non-zero, odd number used as the multiplier
     * @param object
     *            the Object to create a {@code hashCode} for
     * @param testTransients
     *            whether to include transient fields
     * @return int hash code
     * @throws IllegalArgumentException
     *             if the Object is {@code null}
     * @throws IllegalArgumentException
     *             if the number is zero or even
     *
     * @see HashCodeExclude
     */
    public static int reflectionHashCode(final int initialNonZeroOddNumber, final int multiplierNonZeroOddNumber, final Object object,
            final boolean testTransients) {
        return reflectionHashCode(initialNonZeroOddNumber, multiplierNonZeroOddNumber, object, testTransients, null);
    }

    
 Uses reflection to build a valid hash code from the fields of object. 
 It uses AccessibleObject.setAccessible to gain access to private fields. This means that it will throw a security exception if run under a security manager, if the permissions are not set up correctly. It is also not as efficient as testing explicitly. 
 If the TestTransients parameter is set to true, transient members will be tested, otherwise they are ignored, as they are likely derived fields, and not part of the value of the Object. 

Static fields will not be included. Superclass fields will be included up to and including the specified
superclass. A null superclass is treated as java.lang.Object.


Two randomly chosen, non-zero, odd numbers must be passed in. Ideally these should be different for each class,
however this is not vital. Prime numbers are preferred, especially for the multiplier.

Params:
initialNonZeroOddNumber – 
           a non-zero, odd number used as the initial value. This will be the returned
           value if no fields are found to include in the hash code
multiplierNonZeroOddNumber – 
           a non-zero, odd number used as the multiplier
object –  the Object to create a hashCode for
testTransients – 
           whether to include transient fields
reflectUpToClass –  the superclass to reflect up to (inclusive), may be null
excludeFields – 
           array of field names to exclude from use in calculation of hash code
Type parameters:
<T> – 
           the type of the object involved
Throws:
IllegalArgumentException –  if the Object is null
IllegalArgumentException – 
            if the number is zero or even
See Also:
HashCodeExclude
Returns:
int hash code
Since:
2.0/**
     * <p>
     * Uses reflection to build a valid hash code from the fields of {@code object}.
     * </p>
     *
     * <p>
     * It uses {@code AccessibleObject.setAccessible} to gain access to private fields. This means that it will
     * throw a security exception if run under a security manager, if the permissions are not set up correctly. It is
     * also not as efficient as testing explicitly.
     * </p>
     *
     * <p>
     * If the TestTransients parameter is set to {@code true}, transient members will be tested, otherwise they
     * are ignored, as they are likely derived fields, and not part of the value of the {@code Object}.
     * </p>
     *
     * <p>
     * Static fields will not be included. Superclass fields will be included up to and including the specified
     * superclass. A null superclass is treated as java.lang.Object.
     * </p>
     *
     * <p>
     * Two randomly chosen, non-zero, odd numbers must be passed in. Ideally these should be different for each class,
     * however this is not vital. Prime numbers are preferred, especially for the multiplier.
     * </p>
     *
     * @param <T>
     *            the type of the object involved
     * @param initialNonZeroOddNumber
     *            a non-zero, odd number used as the initial value. This will be the returned
     *            value if no fields are found to include in the hash code
     * @param multiplierNonZeroOddNumber
     *            a non-zero, odd number used as the multiplier
     * @param object
     *            the Object to create a {@code hashCode} for
     * @param testTransients
     *            whether to include transient fields
     * @param reflectUpToClass
     *            the superclass to reflect up to (inclusive), may be {@code null}
     * @param excludeFields
     *            array of field names to exclude from use in calculation of hash code
     * @return int hash code
     * @throws IllegalArgumentException
     *             if the Object is {@code null}
     * @throws IllegalArgumentException
     *             if the number is zero or even
     *
     * @see HashCodeExclude
     * @since 2.0
     */
    public static <T> int reflectionHashCode(final int initialNonZeroOddNumber, final int multiplierNonZeroOddNumber, final T object,
            final boolean testTransients, final Class<? super T> reflectUpToClass, final String... excludeFields) {
        Validate.notNull(object, "The object to build a hash code for must not be null");
        final HashCodeBuilder builder = new HashCodeBuilder(initialNonZeroOddNumber, multiplierNonZeroOddNumber);
        Class<?> clazz = object.getClass();
        reflectionAppend(object, clazz, builder, testTransients, excludeFields);
        while (clazz.getSuperclass() != null && clazz != reflectUpToClass) {
            clazz = clazz.getSuperclass();
            reflectionAppend(object, clazz, builder, testTransients, excludeFields);
        }
        return builder.toHashCode();
    }

    
 Uses reflection to build a valid hash code from the fields of object. 

This constructor uses two hard coded choices for the constants needed to build a hash code.

 It uses AccessibleObject.setAccessible to gain access to private fields. This means that it will throw a security exception if run under a security manager, if the permissions are not set up correctly. It is also not as efficient as testing explicitly. 
 If the TestTransients parameter is set to true, transient members will be tested, otherwise they are ignored, as they are likely derived fields, and not part of the value of the Object. 

Static fields will not be tested. Superclass fields will be included. If no fields are found to include
in the hash code, the result of this method will be constant.

Params:
object –  the Object to create a hashCode for
testTransients – 
           whether to include transient fields
Throws:
IllegalArgumentException –  if the object is null
See Also:
HashCodeExclude
Returns:
int hash code/**
     * <p>
     * Uses reflection to build a valid hash code from the fields of {@code object}.
     * </p>
     *
     * <p>
     * This constructor uses two hard coded choices for the constants needed to build a hash code.
     * </p>
     *
     * <p>
     * It uses {@code AccessibleObject.setAccessible} to gain access to private fields. This means that it will
     * throw a security exception if run under a security manager, if the permissions are not set up correctly. It is
     * also not as efficient as testing explicitly.
     * </p>
     *
     * <P>
     * If the TestTransients parameter is set to {@code true}, transient members will be tested, otherwise they
     * are ignored, as they are likely derived fields, and not part of the value of the {@code Object}.
     * </p>
     *
     * <p>
     * Static fields will not be tested. Superclass fields will be included. If no fields are found to include
     * in the hash code, the result of this method will be constant.
     * </p>
     *
     * @param object
     *            the Object to create a {@code hashCode} for
     * @param testTransients
     *            whether to include transient fields
     * @return int hash code
     * @throws IllegalArgumentException
     *             if the object is {@code null}
     *
     * @see HashCodeExclude
     */
    public static int reflectionHashCode(final Object object, final boolean testTransients) {
        return reflectionHashCode(DEFAULT_INITIAL_VALUE, DEFAULT_MULTIPLIER_VALUE, object,
                testTransients, null);
    }

    
 Uses reflection to build a valid hash code from the fields of object. 

This constructor uses two hard coded choices for the constants needed to build a hash code.

 It uses AccessibleObject.setAccessible to gain access to private fields. This means that it will throw a security exception if run under a security manager, if the permissions are not set up correctly. It is also not as efficient as testing explicitly. 
 Transient members will be not be used, as they are likely derived fields, and not part of the value of the Object. 

Static fields will not be tested. Superclass fields will be included. If no fields are found to include
in the hash code, the result of this method will be constant.

Params:
object –  the Object to create a hashCode for
excludeFields – 
           Collection of String field names to exclude from use in calculation of hash code
Throws:
IllegalArgumentException –  if the object is null
See Also:
HashCodeExclude
Returns:
int hash code/**
     * <p>
     * Uses reflection to build a valid hash code from the fields of {@code object}.
     * </p>
     *
     * <p>
     * This constructor uses two hard coded choices for the constants needed to build a hash code.
     * </p>
     *
     * <p>
     * It uses {@code AccessibleObject.setAccessible} to gain access to private fields. This means that it will
     * throw a security exception if run under a security manager, if the permissions are not set up correctly. It is
     * also not as efficient as testing explicitly.
     * </p>
     *
     * <p>
     * Transient members will be not be used, as they are likely derived fields, and not part of the value of the
     * {@code Object}.
     * </p>
     *
     * <p>
     * Static fields will not be tested. Superclass fields will be included. If no fields are found to include
     * in the hash code, the result of this method will be constant.
     * </p>
     *
     * @param object
     *            the Object to create a {@code hashCode} for
     * @param excludeFields
     *            Collection of String field names to exclude from use in calculation of hash code
     * @return int hash code
     * @throws IllegalArgumentException
     *             if the object is {@code null}
     *
     * @see HashCodeExclude
     */
    public static int reflectionHashCode(final Object object, final Collection<String> excludeFields) {
        return reflectionHashCode(object, ReflectionToStringBuilder.toNoNullStringArray(excludeFields));
    }

    // -------------------------------------------------------------------------

    
 Uses reflection to build a valid hash code from the fields of object. 

This constructor uses two hard coded choices for the constants needed to build a hash code.

 It uses AccessibleObject.setAccessible to gain access to private fields. This means that it will throw a security exception if run under a security manager, if the permissions are not set up correctly. It is also not as efficient as testing explicitly. 
 Transient members will be not be used, as they are likely derived fields, and not part of the value of the Object. 

Static fields will not be tested. Superclass fields will be included. If no fields are found to include
in the hash code, the result of this method will be constant.

Params:
object –  the Object to create a hashCode for
excludeFields – 
           array of field names to exclude from use in calculation of hash code
Throws:
IllegalArgumentException –  if the object is null
See Also:
HashCodeExclude
Returns:
int hash code/**
     * <p>
     * Uses reflection to build a valid hash code from the fields of {@code object}.
     * </p>
     *
     * <p>
     * This constructor uses two hard coded choices for the constants needed to build a hash code.
     * </p>
     *
     * <p>
     * It uses {@code AccessibleObject.setAccessible} to gain access to private fields. This means that it will
     * throw a security exception if run under a security manager, if the permissions are not set up correctly. It is
     * also not as efficient as testing explicitly.
     * </p>
     *
     * <p>
     * Transient members will be not be used, as they are likely derived fields, and not part of the value of the
     * {@code Object}.
     * </p>
     *
     * <p>
     * Static fields will not be tested. Superclass fields will be included. If no fields are found to include
     * in the hash code, the result of this method will be constant.
     * </p>
     *
     * @param object
     *            the Object to create a {@code hashCode} for
     * @param excludeFields
     *            array of field names to exclude from use in calculation of hash code
     * @return int hash code
     * @throws IllegalArgumentException
     *             if the object is {@code null}
     *
     * @see HashCodeExclude
     */
    public static int reflectionHashCode(final Object object, final String... excludeFields) {
        return reflectionHashCode(DEFAULT_INITIAL_VALUE, DEFAULT_MULTIPLIER_VALUE, object, false,
                null, excludeFields);
    }

    

Registers the given object. Used by the reflection methods to avoid infinite loops.

Params:
value – 
           The object to register./**
     * <p>
     * Registers the given object. Used by the reflection methods to avoid infinite loops.
     * </p>
     *
     * @param value
     *            The object to register.
     */
    private static void register(final Object value) {
        Set<IDKey> registry = getRegistry();
        if (registry == null) {
            registry = new HashSet<>();
            REGISTRY.set(registry);
        }
        registry.add(new IDKey(value));
    }

    

Unregisters the given object.


Used by the reflection methods to avoid infinite loops.
Params:
value – 
           The object to unregister.
Since:
2.3/**
     * <p>
     * Unregisters the given object.
     * </p>
     *
     * <p>
     * Used by the reflection methods to avoid infinite loops.
     *
     * @param value
     *            The object to unregister.
     * @since 2.3
     */
    private static void unregister(final Object value) {
        final Set<IDKey> registry = getRegistry();
        if (registry != null) {
            registry.remove(new IDKey(value));
            if (registry.isEmpty()) {
                REGISTRY.remove();
            }
        }
    }

    
Constant to use in building the hashCode.
/**
     * Constant to use in building the hashCode.
     */
    private final int iConstant;

    
Running total of the hashCode.
/**
     * Running total of the hashCode.
     */
    private int iTotal = 0;

    
 Uses two hard coded choices for the constants needed to build a hashCode. 
/**
     * <p>
     * Uses two hard coded choices for the constants needed to build a {@code hashCode}.
     * </p>
     */
    public HashCodeBuilder() {
        iConstant = 37;
        iTotal = 17;
    }

    

Two randomly chosen, odd numbers must be passed in. Ideally these should be different for each class,
however this is not vital.


Prime numbers are preferred, especially for the multiplier.

Params:
initialOddNumber – 
           an odd number used as the initial value
multiplierOddNumber – 
           an odd number used as the multiplier
Throws:
IllegalArgumentException – 
            if the number is even/**
     * <p>
     * Two randomly chosen, odd numbers must be passed in. Ideally these should be different for each class,
     * however this is not vital.
     * </p>
     *
     * <p>
     * Prime numbers are preferred, especially for the multiplier.
     * </p>
     *
     * @param initialOddNumber
     *            an odd number used as the initial value
     * @param multiplierOddNumber
     *            an odd number used as the multiplier
     * @throws IllegalArgumentException
     *             if the number is even
     */
    public HashCodeBuilder(final int initialOddNumber, final int multiplierOddNumber) {
        Validate.isTrue(initialOddNumber % 2 != 0, "HashCodeBuilder requires an odd initial value");
        Validate.isTrue(multiplierOddNumber % 2 != 0, "HashCodeBuilder requires an odd multiplier");
        iConstant = multiplierOddNumber;
        iTotal = initialOddNumber;
    }

    
 Append a hashCode for a boolean. 
 This adds 1 when true, and 0 when false to the hashCode. 
 This is in contrast to the standard java.lang.Boolean.hashCode handling, which computes a hashCode value of 1231 for java.lang.Boolean instances that represent true or 1237 for java.lang.Boolean instances that represent false. 

This is in accordance with the Effective Java design.

Params:
value –  the boolean to add to the hashCode
Returns:
this/**
     * <p>
     * Append a {@code hashCode} for a {@code boolean}.
     * </p>
     * <p>
     * This adds {@code 1} when true, and {@code 0} when false to the {@code hashCode}.
     * </p>
     * <p>
     * This is in contrast to the standard {@code java.lang.Boolean.hashCode} handling, which computes
     * a {@code hashCode} value of {@code 1231} for {@code java.lang.Boolean} instances
     * that represent {@code true} or {@code 1237} for {@code java.lang.Boolean} instances
     * that represent {@code false}.
     * </p>
     * <p>
     * This is in accordance with the <i>Effective Java</i> design.
     * </p>
     *
     * @param value
     *            the boolean to add to the {@code hashCode}
     * @return this
     */
    public HashCodeBuilder append(final boolean value) {
        iTotal = iTotal * iConstant + (value ? 0 : 1);
        return this;
    }

    
 Append a hashCode for a boolean array. 
Params:
array –  the array to add to the hashCode
Returns:
this/**
     * <p>
     * Append a {@code hashCode} for a {@code boolean} array.
     * </p>
     *
     * @param array
     *            the array to add to the {@code hashCode}
     * @return this
     */
    public HashCodeBuilder append(final boolean[] array) {
        if (array == null) {
            iTotal = iTotal * iConstant;
        } else {
            for (final boolean element : array) {
                append(element);
            }
        }
        return this;
    }

    // -------------------------------------------------------------------------

    
 Append a hashCode for a byte. 
Params:
value –  the byte to add to the hashCode
Returns:
this/**
     * <p>
     * Append a {@code hashCode} for a {@code byte}.
     * </p>
     *
     * @param value
     *            the byte to add to the {@code hashCode}
     * @return this
     */
    public HashCodeBuilder append(final byte value) {
        iTotal = iTotal * iConstant + value;
        return this;
    }

    // -------------------------------------------------------------------------

    
 Append a hashCode for a byte array. 
Params:
array –  the array to add to the hashCode
Returns:
this/**
     * <p>
     * Append a {@code hashCode} for a {@code byte} array.
     * </p>
     *
     * @param array
     *            the array to add to the {@code hashCode}
     * @return this
     */
    public HashCodeBuilder append(final byte[] array) {
        if (array == null) {
            iTotal = iTotal * iConstant;
        } else {
            for (final byte element : array) {
                append(element);
            }
        }
        return this;
    }

    
 Append a hashCode for a char. 
Params:
value –  the char to add to the hashCode
Returns:
this/**
     * <p>
     * Append a {@code hashCode} for a {@code char}.
     * </p>
     *
     * @param value
     *            the char to add to the {@code hashCode}
     * @return this
     */
    public HashCodeBuilder append(final char value) {
        iTotal = iTotal * iConstant + value;
        return this;
    }

    
 Append a hashCode for a char array. 
Params:
array –  the array to add to the hashCode
Returns:
this/**
     * <p>
     * Append a {@code hashCode} for a {@code char} array.
     * </p>
     *
     * @param array
     *            the array to add to the {@code hashCode}
     * @return this
     */
    public HashCodeBuilder append(final char[] array) {
        if (array == null) {
            iTotal = iTotal * iConstant;
        } else {
            for (final char element : array) {
                append(element);
            }
        }
        return this;
    }

    
 Append a hashCode for a double. 
Params:
value –  the double to add to the hashCode
Returns:
this/**
     * <p>
     * Append a {@code hashCode} for a {@code double}.
     * </p>
     *
     * @param value
     *            the double to add to the {@code hashCode}
     * @return this
     */
    public HashCodeBuilder append(final double value) {
        return append(Double.doubleToLongBits(value));
    }

    
 Append a hashCode for a double array. 
Params:
array –  the array to add to the hashCode
Returns:
this/**
     * <p>
     * Append a {@code hashCode} for a {@code double} array.
     * </p>
     *
     * @param array
     *            the array to add to the {@code hashCode}
     * @return this
     */
    public HashCodeBuilder append(final double[] array) {
        if (array == null) {
            iTotal = iTotal * iConstant;
        } else {
            for (final double element : array) {
                append(element);
            }
        }
        return this;
    }

    
 Append a hashCode for a float. 
Params:
value –  the float to add to the hashCode
Returns:
this/**
     * <p>
     * Append a {@code hashCode} for a {@code float}.
     * </p>
     *
     * @param value
     *            the float to add to the {@code hashCode}
     * @return this
     */
    public HashCodeBuilder append(final float value) {
        iTotal = iTotal * iConstant + Float.floatToIntBits(value);
        return this;
    }

    
 Append a hashCode for a float array. 
Params:
array –  the array to add to the hashCode
Returns:
this/**
     * <p>
     * Append a {@code hashCode} for a {@code float} array.
     * </p>
     *
     * @param array
     *            the array to add to the {@code hashCode}
     * @return this
     */
    public HashCodeBuilder append(final float[] array) {
        if (array == null) {
            iTotal = iTotal * iConstant;
        } else {
            for (final float element : array) {
                append(element);
            }
        }
        return this;
    }

    
 Append a hashCode for an int. 
Params:
value –  the int to add to the hashCode
Returns:
this/**
     * <p>
     * Append a {@code hashCode} for an {@code int}.
     * </p>
     *
     * @param value
     *            the int to add to the {@code hashCode}
     * @return this
     */
    public HashCodeBuilder append(final int value) {
        iTotal = iTotal * iConstant + value;
        return this;
    }

    
 Append a hashCode for an int array. 
Params:
array –  the array to add to the hashCode
Returns:
this/**
     * <p>
     * Append a {@code hashCode} for an {@code int} array.
     * </p>
     *
     * @param array
     *            the array to add to the {@code hashCode}
     * @return this
     */
    public HashCodeBuilder append(final int[] array) {
        if (array == null) {
            iTotal = iTotal * iConstant;
        } else {
            for (final int element : array) {
                append(element);
            }
        }
        return this;
    }

    
 Append a hashCode for a long. 
Params:
value –  the long to add to the hashCode
Returns:
this/**
     * <p>
     * Append a {@code hashCode} for a {@code long}.
     * </p>
     *
     * @param value
     *            the long to add to the {@code hashCode}
     * @return this
     */
    // NOTE: This method uses >> and not >>> as Effective Java and
    //       Long.hashCode do. Ideally we should switch to >>> at
    //       some stage. There are backwards compat issues, so
    //       that will have to wait for the time being. cf LANG-342.
    public HashCodeBuilder append(final long value) {
        iTotal = iTotal * iConstant + ((int) (value ^ (value >> 32)));
        return this;
    }

    
 Append a hashCode for a long array. 
Params:
array –  the array to add to the hashCode
Returns:
this/**
     * <p>
     * Append a {@code hashCode} for a {@code long} array.
     * </p>
     *
     * @param array
     *            the array to add to the {@code hashCode}
     * @return this
     */
    public HashCodeBuilder append(final long[] array) {
        if (array == null) {
            iTotal = iTotal * iConstant;
        } else {
            for (final long element : array) {
                append(element);
            }
        }
        return this;
    }

    
 Append a hashCode for an Object. 
Params:
object –  the Object to add to the hashCode
Returns:
this/**
     * <p>
     * Append a {@code hashCode} for an {@code Object}.
     * </p>
     *
     * @param object
     *            the Object to add to the {@code hashCode}
     * @return this
     */
    public HashCodeBuilder append(final Object object) {
        if (object == null) {
            iTotal = iTotal * iConstant;

        } else {
            if (object.getClass().isArray()) {
                // factor out array case in order to keep method small enough
                // to be inlined
                appendArray(object);
            } else {
                iTotal = iTotal * iConstant + object.hashCode();
            }
        }
        return this;
    }

    
 Append a hashCode for an array. 
Params:
object –  the array to add to the hashCode/**
     * <p>
     * Append a {@code hashCode} for an array.
     * </p>
     *
     * @param object
     *            the array to add to the {@code hashCode}
     */
    private void appendArray(final Object object) {
        // 'Switch' on type of array, to dispatch to the correct handler
        // This handles multi dimensional arrays
        if (object instanceof long[]) {
            append((long[]) object);
        } else if (object instanceof int[]) {
            append((int[]) object);
        } else if (object instanceof short[]) {
            append((short[]) object);
        } else if (object instanceof char[]) {
            append((char[]) object);
        } else if (object instanceof byte[]) {
            append((byte[]) object);
        } else if (object instanceof double[]) {
            append((double[]) object);
        } else if (object instanceof float[]) {
            append((float[]) object);
        } else if (object instanceof boolean[]) {
            append((boolean[]) object);
        } else {
            // Not an array of primitives
            append((Object[]) object);
        }
    }

    
 Append a hashCode for an Object array. 
Params:
array –  the array to add to the hashCode
Returns:
this/**
     * <p>
     * Append a {@code hashCode} for an {@code Object} array.
     * </p>
     *
     * @param array
     *            the array to add to the {@code hashCode}
     * @return this
     */
    public HashCodeBuilder append(final Object[] array) {
        if (array == null) {
            iTotal = iTotal * iConstant;
        } else {
            for (final Object element : array) {
                append(element);
            }
        }
        return this;
    }

    
 Append a hashCode for a short. 
Params:
value –  the short to add to the hashCode
Returns:
this/**
     * <p>
     * Append a {@code hashCode} for a {@code short}.
     * </p>
     *
     * @param value
     *            the short to add to the {@code hashCode}
     * @return this
     */
    public HashCodeBuilder append(final short value) {
        iTotal = iTotal * iConstant + value;
        return this;
    }

    
 Append a hashCode for a short array. 
Params:
array –  the array to add to the hashCode
Returns:
this/**
     * <p>
     * Append a {@code hashCode} for a {@code short} array.
     * </p>
     *
     * @param array
     *            the array to add to the {@code hashCode}
     * @return this
     */
    public HashCodeBuilder append(final short[] array) {
        if (array == null) {
            iTotal = iTotal * iConstant;
        } else {
            for (final short element : array) {
                append(element);
            }
        }
        return this;
    }

    

Adds the result of super.hashCode() to this builder.

Params:
superHashCode –  the result of calling super.hashCode()
Returns:
this HashCodeBuilder, used to chain calls.
Since:
2.0/**
     * <p>
     * Adds the result of super.hashCode() to this builder.
     * </p>
     *
     * @param superHashCode
     *            the result of calling {@code super.hashCode()}
     * @return this HashCodeBuilder, used to chain calls.
     * @since 2.0
     */
    public HashCodeBuilder appendSuper(final int superHashCode) {
        iTotal = iTotal * iConstant + superHashCode;
        return this;
    }

    
 Returns the computed hashCode. 
Returns:
hashCode based on the fields appended/**
     * <p>
     * Returns the computed {@code hashCode}.
     * </p>
     *
     * @return {@code hashCode} based on the fields appended
     */
    public int toHashCode() {
        return iTotal;
    }

    
Returns the computed hashCode. 
Returns:
hashCode based on the fields appended
Since:
3.0/**
     * Returns the computed {@code hashCode}.
     *
     * @return {@code hashCode} based on the fields appended
     *
     * @since 3.0
     */
    @Override
    public Integer build() {
        return Integer.valueOf(toHashCode());
    }

    
 The computed hashCode from toHashCode() is returned due to the likelihood of bugs in mis-calling toHashCode() and the unlikeliness of it mattering what the hashCode for HashCodeBuilder itself is.
Returns:
hashCode based on the fields appended
Since:
2.5/**
     * <p>
     * The computed {@code hashCode} from toHashCode() is returned due to the likelihood
     * of bugs in mis-calling toHashCode() and the unlikeliness of it mattering what the hashCode for
     * HashCodeBuilder itself is.</p>
     *
     * @return {@code hashCode} based on the fields appended
     * @since 2.5
     */
    @Override
    public int hashCode() {
        return toHashCode();
    }

}