HashCodeBuilder.java
/*
* 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.Collection;
import java.util.Comparator;
import java.util.HashSet;
import java.util.Objects;
import java.util.Set;
import org.apache.commons.lang3.ArraySorter;
import org.apache.commons.lang3.ArrayUtils;
import org.apache.commons.lang3.ObjectUtils;
import org.apache.commons.lang3.Validate;
/**
* Assists in implementing {@link Object#hashCode()} methods.
*
* <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="https://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.
*/
private static final int DEFAULT_INITIAL_VALUE = 17;
/**
* 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
*/
private static final ThreadLocal<Set<IDKey>> REGISTRY = ThreadLocal.withInitial(HashSet::new);
/*
* 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.
*
* @return Set the registry of objects being traversed
* @since 2.3
*/
static Set<IDKey> getRegistry() {
return REGISTRY.get();
}
/**
* Returns {@code 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 {@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 {@link 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(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 = ArraySorter.sort(clazz.getDeclaredFields(), 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)) {
builder.append(Reflection.getUnchecked(field, object));
}
}
} finally {
unregister(object);
}
}
/**
* Uses reflection to build a valid hash code from the fields of {@code object}.
*
* <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
* {@link 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 NullPointerException
* 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 {@code object}.
*
* <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 {@link 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 NullPointerException
* 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 {@code object}.
*
* <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 {@link 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 NullPointerException
* 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) {
Objects.requireNonNull(object, "object");
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 {@code object}.
*
* <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 {@link 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 NullPointerException
* 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 {@code object}.
*
* <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
* {@link 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 NullPointerException
* 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 {@code object}.
*
* <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
* {@link 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 NullPointerException
* 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.
*
* @param value
* The object to register.
*/
private static void register(final Object value) {
getRegistry().add(new IDKey(value));
}
/**
* Unregisters the given object.
*
* <p>
* Used by the reflection methods to avoid infinite loops.
* </p>
*
* @param value
* The object to unregister.
* @since 2.3
*/
private static void unregister(final Object value) {
final Set<IDKey> registry = getRegistry();
registry.remove(new IDKey(value));
if (registry.isEmpty()) {
REGISTRY.remove();
}
}
/**
* Constant to use in building the hashCode.
*/
private final int iConstant;
/**
* Running total of the hashCode.
*/
private int iTotal;
/**
* Uses two hard coded choices for the constants needed to build a {@code hashCode}.
*/
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.
*
* <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 {@code hashCode} for a {@code boolean}.
*
* <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 {@link Boolean#hashCode()} handling, which computes
* a {@code hashCode} value of {@code 1231} for {@link Boolean} instances
* that represent {@code true} or {@code 1237} for {@link Boolean} instances
* that represent {@code false}.
* </p>
* <p>
* This is in accordance with the <em>Effective Java</em> design.
* </p>
*
* @param value
* the boolean to add to the {@code hashCode}
* @return {@code this} instance.
*/
public HashCodeBuilder append(final boolean value) {
iTotal = iTotal * iConstant + (value ? 0 : 1);
return this;
}
/**
* Append a {@code hashCode} for a {@code boolean} array.
*
* @param array
* the array to add to the {@code hashCode}
* @return {@code this} instance.
*/
public HashCodeBuilder append(final boolean[] array) {
if (array == null) {
iTotal = iTotal * iConstant;
} else {
for (final boolean element : array) {
append(element);
}
}
return this;
}
/**
* Append a {@code hashCode} for a {@code byte}.
*
* @param value
* the byte to add to the {@code hashCode}
* @return {@code this} instance.
*/
public HashCodeBuilder append(final byte value) {
iTotal = iTotal * iConstant + value;
return this;
}
/**
* Append a {@code hashCode} for a {@code byte} array.
*
* @param array
* the array to add to the {@code hashCode}
* @return {@code this} instance.
*/
public HashCodeBuilder append(final byte[] array) {
if (array == null) {
iTotal = iTotal * iConstant;
} else {
for (final byte element : array) {
append(element);
}
}
return this;
}
/**
* Append a {@code hashCode} for a {@code char}.
*
* @param value
* the char to add to the {@code hashCode}
* @return {@code this} instance.
*/
public HashCodeBuilder append(final char value) {
iTotal = iTotal * iConstant + value;
return this;
}
/**
* Append a {@code hashCode} for a {@code char} array.
*
* @param array
* the array to add to the {@code hashCode}
* @return {@code this} instance.
*/
public HashCodeBuilder append(final char[] array) {
if (array == null) {
iTotal = iTotal * iConstant;
} else {
for (final char element : array) {
append(element);
}
}
return this;
}
/**
* Append a {@code hashCode} for a {@code double}.
*
* @param value
* the double to add to the {@code hashCode}
* @return {@code this} instance.
*/
public HashCodeBuilder append(final double value) {
return append(Double.doubleToLongBits(value));
}
/**
* Append a {@code hashCode} for a {@code double} array.
*
* @param array
* the array to add to the {@code hashCode}
* @return {@code this} instance.
*/
public HashCodeBuilder append(final double[] array) {
if (array == null) {
iTotal = iTotal * iConstant;
} else {
for (final double element : array) {
append(element);
}
}
return this;
}
/**
* Append a {@code hashCode} for a {@code float}.
*
* @param value
* the float to add to the {@code hashCode}
* @return {@code this} instance.
*/
public HashCodeBuilder append(final float value) {
iTotal = iTotal * iConstant + Float.floatToIntBits(value);
return this;
}
/**
* Append a {@code hashCode} for a {@code float} array.
*
* @param array
* the array to add to the {@code hashCode}
* @return {@code this} instance.
*/
public HashCodeBuilder append(final float[] array) {
if (array == null) {
iTotal = iTotal * iConstant;
} else {
for (final float element : array) {
append(element);
}
}
return this;
}
/**
* Append a {@code hashCode} for an {@code int}.
*
* @param value
* the int to add to the {@code hashCode}
* @return {@code this} instance.
*/
public HashCodeBuilder append(final int value) {
iTotal = iTotal * iConstant + value;
return this;
}
/**
* Append a {@code hashCode} for an {@code int} array.
*
* @param array
* the array to add to the {@code hashCode}
* @return {@code this} instance.
*/
public HashCodeBuilder append(final int[] array) {
if (array == null) {
iTotal = iTotal * iConstant;
} else {
for (final int element : array) {
append(element);
}
}
return this;
}
/**
* Append a {@code hashCode} for a {@code long}.
*
* @param value
* the long to add to the {@code hashCode}
* @return {@code this} instance.
*/
// 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 {@code hashCode} for a {@code long} array.
*
* @param array
* the array to add to the {@code hashCode}
* @return {@code this} instance.
*/
public HashCodeBuilder append(final long[] array) {
if (array == null) {
iTotal = iTotal * iConstant;
} else {
for (final long element : array) {
append(element);
}
}
return this;
}
/**
* Append a {@code hashCode} for an {@link Object}.
*
* @param object
* the Object to add to the {@code hashCode}
* @return {@code this} instance.
*/
public HashCodeBuilder append(final Object object) {
if (object == null) {
iTotal = iTotal * iConstant;
} else if (ObjectUtils.isArray(object)) {
// 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 {@code hashCode} for an {@link Object} array.
*
* @param array
* the array to add to the {@code hashCode}
* @return {@code this} instance.
*/
public HashCodeBuilder append(final Object[] array) {
if (array == null) {
iTotal = iTotal * iConstant;
} else {
for (final Object element : array) {
append(element);
}
}
return this;
}
/**
* Append a {@code hashCode} for a {@code short}.
*
* @param value
* the short to add to the {@code hashCode}
* @return {@code this} instance.
*/
public HashCodeBuilder append(final short value) {
iTotal = iTotal * iConstant + value;
return this;
}
/**
* Append a {@code hashCode} for a {@code short} array.
*
* @param array
* the array to add to the {@code hashCode}
* @return {@code this} instance.
*/
public HashCodeBuilder append(final short[] array) {
if (array == null) {
iTotal = iTotal * iConstant;
} else {
for (final short element : array) {
append(element);
}
}
return this;
}
/**
* Append a {@code hashCode} for an array.
*
* @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 multidimensional 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);
}
}
/**
* Adds the result of super.hashCode() to this builder.
*
* @param superHashCode
* the result of calling {@code super.hashCode()}
* @return {@code this} instance.
* @since 2.0
*/
public HashCodeBuilder appendSuper(final int superHashCode) {
iTotal = iTotal * iConstant + superHashCode;
return this;
}
/**
* Returns the computed {@code hashCode}.
*
* @return {@code hashCode} based on the fields appended
* @since 3.0
*/
@Override
public Integer build() {
return Integer.valueOf(toHashCode());
}
/**
* Implements equals using the hash code.
*
* @since 3.13.0
*/
@Override
public boolean equals(final Object obj) {
if (this == obj) {
return true;
}
if (!(obj instanceof HashCodeBuilder)) {
return false;
}
final HashCodeBuilder other = (HashCodeBuilder) obj;
return iTotal == other.iTotal;
}
/**
* 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.
*
* @return {@code hashCode} based on the fields appended
* @since 2.5
*/
@Override
public int hashCode() {
return toHashCode();
}
/**
* Returns the computed {@code hashCode}.
*
* @return {@code hashCode} based on the fields appended
*/
public int toHashCode() {
return iTotal;
}
}