/*
 * 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.lang.builder;

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

import org.apache.commons.lang.ArrayUtils;

 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 hashcode 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);
}

Author:
Apache Software Foundation, Gary Gregory, Pete Gieser
Since:
1.0
Version:
$Id: HashCodeBuilder.java 1057009 2011-01-09 19:48:06Z niallp $/**
 * <p>
 * Assists in implementing {@link Object#hashCode()} methods.
 * </p>
 * 
 * <p>
 * This class enables a good <code>hashCode</code> method to be built for any class. It follows the rules laid out in
 * the book <a href="http://java.sun.com/docs/books/effective/index.html">Effective Java</a> by Joshua Bloch. Writing a
 * good <code>hashCode</code> 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 hashcode of 674, namely 17 * 37 + 45. 
 * </p>
 * 
 * <p>
 * All relevant fields from the object should be included in the <code>hashCode</code> method. Derived fields may be
 * excluded. In general, any field used in the <code>equals</code> method must be used in the <code>hashCode</code>
 * 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()</code> 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</code>, uses <code>AccessibleObject.setAccessible</code>
 * 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>
 * 
 * @author Apache Software Foundation
 * @author Gary Gregory
 * @author Pete Gieser
 * @since 1.0
 * @version $Id: HashCodeBuilder.java 1057009 2011-01-09 19:48:06Z niallp $
 */
public class HashCodeBuilder {
    

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 REGISTRY = new ThreadLocal();

    /*
     * N.B. 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 hashcode 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.indentityHashCode()
     * 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 getRegistry() {
        return (Set) 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</code> 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</code> if the registry contains the given object.
     * @since 2.3
     */
    static boolean isRegistered(Object value) {
        Set 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</code>.
     * </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(Object object, Class clazz, HashCodeBuilder builder, boolean useTransients,
            String[] excludeFields) {
        if (isRegistered(object)) {
            return;
        }
        try {
            register(object);
            Field[] fields = clazz.getDeclaredFields();
            AccessibleObject.setAccessible(fields, true);
            for (int i = 0; i < fields.length; i++) {
                Field field = fields[i];
                if (!ArrayUtils.contains(excludeFields, field.getName())
                    && (field.getName().indexOf('$') == -1)
                    && (useTransients || !Modifier.isTransient(field.getModifiers()))
                    && (!Modifier.isStatic(field.getModifiers()))) {
                    try {
                        Object fieldValue = field.get(object);
                        builder.append(fieldValue);
                    } catch (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);
        }
    }

    

This method uses reflection to build a valid 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.


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
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
Returns:
int hash code/**
     * <p>
     * This method uses reflection to build a valid hash code.
     * </p>
     * 
     * <p>
     * It uses <code>AccessibleObject.setAccessible</code> 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</code>.
     * </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
     * @param multiplierNonZeroOddNumber
     *            a non-zero, odd number used as the multiplier
     * @param object
     *            the Object to create a <code>hashCode</code> for
     * @return int hash code
     * @throws IllegalArgumentException
     *             if the Object is <code>null</code>
     * @throws IllegalArgumentException
     *             if the number is zero or even
     */
    public static int reflectionHashCode(int initialNonZeroOddNumber, int multiplierNonZeroOddNumber, Object object) {
        return reflectionHashCode(initialNonZeroOddNumber, multiplierNonZeroOddNumber, object, false, null, null);
    }

    

This method uses reflection to build a valid 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.


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
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
Returns:
int hash code/**
     * <p>
     * This method uses reflection to build a valid hash code.
     * </p>
     * 
     * <p>
     * It uses <code>AccessibleObject.setAccessible</code> 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</code>, 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</code>.
     * </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
     * @param multiplierNonZeroOddNumber
     *            a non-zero, odd number used as the multiplier
     * @param object
     *            the Object to create a <code>hashCode</code> for
     * @param testTransients
     *            whether to include transient fields
     * @return int hash code
     * @throws IllegalArgumentException
     *             if the Object is <code>null</code>
     * @throws IllegalArgumentException
     *             if the number is zero or even
     */
    public static int reflectionHashCode(int initialNonZeroOddNumber, int multiplierNonZeroOddNumber, Object object,
            boolean testTransients) {
        return reflectionHashCode(initialNonZeroOddNumber, multiplierNonZeroOddNumber, object, testTransients, null,
                null);
    }

    
Calls reflectionHashCode(int, int, Object, boolean, Class, String[]) with excludeFields set to null.
Params:
initialNonZeroOddNumber – 
           a non-zero, odd number used as the initial value
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
Returns:
int hash code/**
     * Calls {@link #reflectionHashCode(int, int, Object, boolean, Class, String[])} with excludeFields set to
     * <code>null</code>.
     * 
     * @param initialNonZeroOddNumber
     *            a non-zero, odd number used as the initial value
     * @param multiplierNonZeroOddNumber
     *            a non-zero, odd number used as the multiplier
     * @param object
     *            the Object to create a <code>hashCode</code> for
     * @param testTransients
     *            whether to include transient fields
     * @param reflectUpToClass
     *            the superclass to reflect up to (inclusive), may be <code>null</code>
     * @return int hash code
     */
    public static int reflectionHashCode(int initialNonZeroOddNumber, int multiplierNonZeroOddNumber, Object object,
            boolean testTransients, Class reflectUpToClass) {
        return reflectionHashCode(initialNonZeroOddNumber, multiplierNonZeroOddNumber, object, testTransients,
                reflectUpToClass, null);
    }

    

This method uses reflection to build a valid 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 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
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
Throws:
IllegalArgumentException – 
            if the Object is null
IllegalArgumentException – 
            if the number is zero or even
Returns:
int hash code
Since:
2.0/**
     * <p>
     * This method uses reflection to build a valid hash code.
     * </p>
     * 
     * <p>
     * It uses <code>AccessibleObject.setAccessible</code> 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</code>, 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</code>.
     * </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 initialNonZeroOddNumber
     *            a non-zero, odd number used as the initial value
     * @param multiplierNonZeroOddNumber
     *            a non-zero, odd number used as the multiplier
     * @param object
     *            the Object to create a <code>hashCode</code> for
     * @param testTransients
     *            whether to include transient fields
     * @param reflectUpToClass
     *            the superclass to reflect up to (inclusive), may be <code>null</code>
     * @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</code>
     * @throws IllegalArgumentException
     *             if the number is zero or even
     * @since 2.0
     */
    public static int reflectionHashCode(int initialNonZeroOddNumber, int multiplierNonZeroOddNumber, Object object,
            boolean testTransients, Class reflectUpToClass, String[] excludeFields) {

        if (object == null) {
            throw new IllegalArgumentException("The object to build a hash code for must not be null");
        }
        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();
    }

    

This method uses reflection to build a valid hash code.


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.

Params:
object – 
           the Object to create a hashCode for
Throws:
IllegalArgumentException – 
            if the object is null
Returns:
int hash code/**
     * <p>
     * This method uses reflection to build a valid hash code.
     * </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</code> 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</code>.
     * </p>
     * 
     * <p>
     * Static fields will not be tested. Superclass fields will be included.
     * </p>
     * 
     * @param object
     *            the Object to create a <code>hashCode</code> for
     * @return int hash code
     * @throws IllegalArgumentException
     *             if the object is <code>null</code>
     */
    public static int reflectionHashCode(Object object) {
        return reflectionHashCode(17, 37, object, false, null, null);
    }

    

This method uses reflection to build a valid hash code.


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.

Params:
object – 
           the Object to create a hashCode for
testTransients – 
           whether to include transient fields
Throws:
IllegalArgumentException – 
            if the object is null
Returns:
int hash code/**
     * <p>
     * This method uses reflection to build a valid hash code.
     * </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</code> 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</code>, 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</code>.
     * </p>
     * 
     * <p>
     * Static fields will not be tested. Superclass fields will be included.
     * </p>
     * 
     * @param object
     *            the Object to create a <code>hashCode</code> for
     * @param testTransients
     *            whether to include transient fields
     * @return int hash code
     * @throws IllegalArgumentException
     *             if the object is <code>null</code>
     */
    public static int reflectionHashCode(Object object, boolean testTransients) {
        return reflectionHashCode(17, 37, object, testTransients, null, null);
    }

    

This method uses reflection to build a valid hash code.


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.

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
Returns:
int hash code/**
     * <p>
     * This method uses reflection to build a valid hash code.
     * </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</code> 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</code>.
     * </p>
     * 
     * <p>
     * Static fields will not be tested. Superclass fields will be included.
     * </p>
     * 
     * @param object
     *            the Object to create a <code>hashCode</code> 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</code>
     */
    public static int reflectionHashCode(Object object, Collection /* String */excludeFields) {
        return reflectionHashCode(object, ReflectionToStringBuilder.toNoNullStringArray(excludeFields));
    }

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

    

This method uses reflection to build a valid hash code.


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.

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
Returns:
int hash code/**
     * <p>
     * This method uses reflection to build a valid hash code.
     * </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</code> 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</code>.
     * </p>
     * 
     * <p>
     * Static fields will not be tested. Superclass fields will be included.
     * </p>
     * 
     * @param object
     *            the Object to create a <code>hashCode</code> 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</code>
     */
    public static int reflectionHashCode(Object object, String[] excludeFields) {
        return reflectionHashCode(17, 37, 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.
     */
    static void register(Object value) {
        synchronized (HashCodeBuilder.class) {
            if (getRegistry() == null) {
                REGISTRY.set(new HashSet());
            }
        }
        getRegistry().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
     */
    static void unregister(Object value) {
        Set registry = getRegistry();
        if (registry != null) {
            registry.remove(new IDKey(value));
            synchronized (HashCodeBuilder.class) {
                //read again
                registry = getRegistry();
                if (registry != null && registry.isEmpty()) {
                    REGISTRY.set(null);
                }
            }
        }
    }

    
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</code>.
     * </p>
     */
    public HashCodeBuilder() {
        iConstant = 37;
        iTotal = 17;
    }

    

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
multiplierNonZeroOddNumber – 
           a non-zero, odd number used as the multiplier
Throws:
IllegalArgumentException – 
            if the number is zero or even/**
     * <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.
     * </p>
     * 
     * <p>
     * Prime numbers are preferred, especially for the multiplier.
     * </p>
     * 
     * @param initialNonZeroOddNumber
     *            a non-zero, odd number used as the initial value
     * @param multiplierNonZeroOddNumber
     *            a non-zero, odd number used as the multiplier
     * @throws IllegalArgumentException
     *             if the number is zero or even
     */
    public HashCodeBuilder(int initialNonZeroOddNumber, int multiplierNonZeroOddNumber) {
        if (initialNonZeroOddNumber == 0) {
            throw new IllegalArgumentException("HashCodeBuilder requires a non zero initial value");
        }
        if (initialNonZeroOddNumber % 2 == 0) {
            throw new IllegalArgumentException("HashCodeBuilder requires an odd initial value");
        }
        if (multiplierNonZeroOddNumber == 0) {
            throw new IllegalArgumentException("HashCodeBuilder requires a non zero multiplier");
        }
        if (multiplierNonZeroOddNumber % 2 == 0) {
            throw new IllegalArgumentException("HashCodeBuilder requires an odd multiplier");
        }
        iConstant = multiplierNonZeroOddNumber;
        iTotal = initialNonZeroOddNumber;
    }

    

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</code> for a <code>boolean</code>.
     * </p>
     * <p>
     * This adds <code>1</code> when true, and <code>0</code> when false to the <code>hashCode</code>.
     * </p>
     * <p>
     * This is in contrast to the standard <code>java.lang.Boolean.hashCode</code> handling, which computes
     * a <code>hashCode</code> value of <code>1231</code> for <code>java.lang.Boolean</code> instances
     * that represent <code>true</code> or <code>1237</code> for <code>java.lang.Boolean</code> instances
     * that represent <code>false</code>.
     * </p>
     * <p>
     * This is in accordance with the <quote>Effective Java</quote> design.
     * </p>
     * 
     * @param value
     *            the boolean to add to the <code>hashCode</code>
     * @return this
     */
    public HashCodeBuilder append(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</code> for a <code>boolean</code> array.
     * </p>
     * 
     * @param array
     *            the array to add to the <code>hashCode</code>
     * @return this
     */
    public HashCodeBuilder append(boolean[] array) {
        if (array == null) {
            iTotal = iTotal * iConstant;
        } else {
            for (int i = 0; i < array.length; i++) {
                append(array[i]);
            }
        }
        return this;
    }

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

    

Append a hashCode for a byte.

Params:
value – 
           the byte to add to the hashCode
Returns:
this/**
     * <p>
     * Append a <code>hashCode</code> for a <code>byte</code>.
     * </p>
     * 
     * @param value
     *            the byte to add to the <code>hashCode</code>
     * @return this
     */
    public HashCodeBuilder append(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</code> for a <code>byte</code> array.
     * </p>
     * 
     * @param array
     *            the array to add to the <code>hashCode</code>
     * @return this
     */
    public HashCodeBuilder append(byte[] array) {
        if (array == null) {
            iTotal = iTotal * iConstant;
        } else {
            for (int i = 0; i < array.length; i++) {
                append(array[i]);
            }
        }
        return this;
    }

    

Append a hashCode for a char.

Params:
value – 
           the char to add to the hashCode
Returns:
this/**
     * <p>
     * Append a <code>hashCode</code> for a <code>char</code>.
     * </p>
     * 
     * @param value
     *            the char to add to the <code>hashCode</code>
     * @return this
     */
    public HashCodeBuilder append(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</code> for a <code>char</code> array.
     * </p>
     * 
     * @param array
     *            the array to add to the <code>hashCode</code>
     * @return this
     */
    public HashCodeBuilder append(char[] array) {
        if (array == null) {
            iTotal = iTotal * iConstant;
        } else {
            for (int i = 0; i < array.length; i++) {
                append(array[i]);
            }
        }
        return this;
    }

    

Append a hashCode for a double.

Params:
value – 
           the double to add to the hashCode
Returns:
this/**
     * <p>
     * Append a <code>hashCode</code> for a <code>double</code>.
     * </p>
     * 
     * @param value
     *            the double to add to the <code>hashCode</code>
     * @return this
     */
    public HashCodeBuilder append(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</code> for a <code>double</code> array.
     * </p>
     * 
     * @param array
     *            the array to add to the <code>hashCode</code>
     * @return this
     */
    public HashCodeBuilder append(double[] array) {
        if (array == null) {
            iTotal = iTotal * iConstant;
        } else {
            for (int i = 0; i < array.length; i++) {
                append(array[i]);
            }
        }
        return this;
    }

    

Append a hashCode for a float.

Params:
value – 
           the float to add to the hashCode
Returns:
this/**
     * <p>
     * Append a <code>hashCode</code> for a <code>float</code>.
     * </p>
     * 
     * @param value
     *            the float to add to the <code>hashCode</code>
     * @return this
     */
    public HashCodeBuilder append(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</code> for a <code>float</code> array.
     * </p>
     * 
     * @param array
     *            the array to add to the <code>hashCode</code>
     * @return this
     */
    public HashCodeBuilder append(float[] array) {
        if (array == null) {
            iTotal = iTotal * iConstant;
        } else {
            for (int i = 0; i < array.length; i++) {
                append(array[i]);
            }
        }
        return this;
    }

    

Append a hashCode for an int.

Params:
value – 
           the int to add to the hashCode
Returns:
this/**
     * <p>
     * Append a <code>hashCode</code> for an <code>int</code>.
     * </p>
     * 
     * @param value
     *            the int to add to the <code>hashCode</code>
     * @return this
     */
    public HashCodeBuilder append(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</code> for an <code>int</code> array.
     * </p>
     * 
     * @param array
     *            the array to add to the <code>hashCode</code>
     * @return this
     */
    public HashCodeBuilder append(int[] array) {
        if (array == null) {
            iTotal = iTotal * iConstant;
        } else {
            for (int i = 0; i < array.length; i++) {
                append(array[i]);
            }
        }
        return this;
    }

    

Append a hashCode for a long.

Params:
value – 
           the long to add to the hashCode
Returns:
this/**
     * <p>
     * Append a <code>hashCode</code> for a <code>long</code>.
     * </p>
     * 
     * @param value
     *            the long to add to the <code>hashCode</code>
     * @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(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</code> for a <code>long</code> array.
     * </p>
     * 
     * @param array
     *            the array to add to the <code>hashCode</code>
     * @return this
     */
    public HashCodeBuilder append(long[] array) {
        if (array == null) {
            iTotal = iTotal * iConstant;
        } else {
            for (int i = 0; i < array.length; i++) {
                append(array[i]);
            }
        }
        return this;
    }

    

Append a hashCode for an Object.

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

        } else {
            if(object.getClass().isArray()) {
                // '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);
                }
            } else {
                iTotal = iTotal * iConstant + object.hashCode();
            }
        }
        return this;
    }

    

Append a hashCode for an Object array.

Params:
array – 
           the array to add to the hashCode
Returns:
this/**
     * <p>
     * Append a <code>hashCode</code> for an <code>Object</code> array.
     * </p>
     * 
     * @param array
     *            the array to add to the <code>hashCode</code>
     * @return this
     */
    public HashCodeBuilder append(Object[] array) {
        if (array == null) {
            iTotal = iTotal * iConstant;
        } else {
            for (int i = 0; i < array.length; i++) {
                append(array[i]);
            }
        }
        return this;
    }

    

Append a hashCode for a short.

Params:
value – 
           the short to add to the hashCode
Returns:
this/**
     * <p>
     * Append a <code>hashCode</code> for a <code>short</code>.
     * </p>
     * 
     * @param value
     *            the short to add to the <code>hashCode</code>
     * @return this
     */
    public HashCodeBuilder append(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</code> for a <code>short</code> array.
     * </p>
     * 
     * @param array
     *            the array to add to the <code>hashCode</code>
     * @return this
     */
    public HashCodeBuilder append(short[] array) {
        if (array == null) {
            iTotal = iTotal * iConstant;
        } else {
            for (int i = 0; i < array.length; i++) {
                append(array[i]);
            }
        }
        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()</code>
     * @return this HashCodeBuilder, used to chain calls.
     * @since 2.0
     */
    public HashCodeBuilder appendSuper(int superHashCode) {
        iTotal = iTotal * iConstant + superHashCode;
        return this;
    }

    

Return the computed hashCode.

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

    

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

}