org.apache.commons.lang.builder.HashCodeBuilder Maven / Gradle / Ivy
/*
* 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 {@link 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 {@link #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
* @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
*/
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.
*
*
* @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.
*
*
* @param value
* The object to lookup in the registry.
* @return boolean true 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.
*
*
* @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.
*
*
* @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 hashCode for
* @return int hash code
* @throws IllegalArgumentException
* if the Object is null
* @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.
*
*
* @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 hashCode for
* @param testTransients
* whether to include transient fields
* @return int hash code
* @throws IllegalArgumentException
* if the Object is null
* @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 {@link #reflectionHashCode(int, int, Object, boolean, Class, String[])} with excludeFields set to
* null.
*
* @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 hashCode for
* @param testTransients
* whether to include transient fields
* @param reflectUpToClass
* the superclass to reflect up to (inclusive), may be null
* @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.
*
*
* @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 hashCode for
* @param testTransients
* whether to include transient fields
* @param reflectUpToClass
* the superclass to reflect up to (inclusive), may be 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 null
* @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.
*
*
* @param object
* the Object to create a hashCode for
* @return int hash code
* @throws IllegalArgumentException
* if the object is null
*/
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.
*
*
* @param object
* the Object to create a hashCode for
* @param testTransients
* whether to include transient fields
* @return int hash code
* @throws IllegalArgumentException
* if the object is null
*/
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.
*
*
* @param object
* the Object to create a 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 null
*/
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.
*
*
* @param object
* the Object to create a 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 null
*/
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.
*
*
* @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.
*
* @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.
*/
private final int iConstant;
/**
* Running total of the hashCode.
*/
private int iTotal = 0;
/**
*
* Uses two hard coded choices for the constants needed to build a hashCode.
*
*/
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.
*
*
* @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.
*
*
* @param value
* the boolean to add to the hashCode
* @return this
*/
public HashCodeBuilder append(boolean value) {
iTotal = iTotal * iConstant + (value ? 0 : 1);
return this;
}
/**
*
* Append a hashCode for a boolean array.
*
*
* @param array
* the array to add to the hashCode
* @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.
*
*
* @param value
* the byte to add to the hashCode
* @return this
*/
public HashCodeBuilder append(byte value) {
iTotal = iTotal * iConstant + value;
return this;
}
// -------------------------------------------------------------------------
/**
*
* Append a hashCode for a byte array.
*
*
* @param array
* the array to add to the hashCode
* @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.
*
*
* @param value
* the char to add to the hashCode
* @return this
*/
public HashCodeBuilder append(char value) {
iTotal = iTotal * iConstant + value;
return this;
}
/**
*
* Append a hashCode for a char array.
*
*
* @param array
* the array to add to the hashCode
* @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.
*
*
* @param value
* the double to add to the hashCode
* @return this
*/
public HashCodeBuilder append(double value) {
return append(Double.doubleToLongBits(value));
}
/**
*
* Append a hashCode for a double array.
*
*
* @param array
* the array to add to the hashCode
* @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.
*
*
* @param value
* the float to add to the hashCode
* @return this
*/
public HashCodeBuilder append(float value) {
iTotal = iTotal * iConstant + Float.floatToIntBits(value);
return this;
}
/**
*
* Append a hashCode for a float array.
*
*
* @param array
* the array to add to the hashCode
* @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.
*
*
* @param value
* the int to add to the hashCode
* @return this
*/
public HashCodeBuilder append(int value) {
iTotal = iTotal * iConstant + value;
return this;
}
/**
*
* Append a hashCode for an int array.
*
*
* @param array
* the array to add to the hashCode
* @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.
*
*
* @param value
* the long to add to the 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(long value) {
iTotal = iTotal * iConstant + ((int) (value ^ (value >> 32)));
return this;
}
/**
*
* Append a hashCode for a long array.
*
*
* @param array
* the array to add to the hashCode
* @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.
*
*
* @param object
* the Object to add to the hashCode
* @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.
*
*
* @param array
* the array to add to the hashCode
* @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.
*
*
* @param value
* the short to add to the hashCode
* @return this
*/
public HashCodeBuilder append(short value) {
iTotal = iTotal * iConstant + value;
return this;
}
/**
*
* Append a hashCode for a short array.
*
*
* @param array
* the array to add to the hashCode
* @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.
*
*
* @param superHashCode
* the result of calling super.hashCode()
* @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.
*
*
* @return hashCode 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.
*
* @return hashCode based on the fields appended
* @since 2.5
*/
public int hashCode() {
return toHashCode();
}
}