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/*
* Copyright (C) 2010 The Guava Authors
*
* Licensed 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 com.google.common.base;
import com.google.common.annotations.Beta;
import com.google.common.annotations.GwtCompatible;
import java.io.Serializable;
/**
* Contains static factory methods for creating {@code Equivalence} instances.
*
* <p>All methods return serializable instances.
*
* @author Bob Lee
* @author Kurt Alfred Kluever
* @author Gregory Kick
* @since 4.0
*/
@Beta
@GwtCompatible
public final class Equivalences {
private Equivalences() {}
/**
* Returns an equivalence that delegates to {@link Object#equals} and {@link Object#hashCode}.
* {@link Equivalence#equivalent} returns {@code true} if both values are null, or if neither
* value is null and {@link Object#equals} returns {@code true}. {@link Equivalence#hash} returns
* {@code 0} if passed a null value.
*
* @since 8.0 (present null-friendly behavior)
* @since 4.0 (otherwise)
*/
public static Equivalence<Object> equals() {
return Equals.INSTANCE;
}
/**
* Returns an equivalence that uses {@code ==} to compare values and {@link
* System#identityHashCode(Object)} to compute the hash code. {@link Equivalence#equivalent}
* returns {@code true} if {@code a == b}, including in the case that a and b are both null.
*/
public static Equivalence<Object> identity() {
return Identity.INSTANCE;
}
private static final class Equals extends Equivalence<Object>
implements Serializable {
static final Equals INSTANCE = new Equals();
@Override protected boolean doEquivalent(Object a, Object b) {
return a.equals(b);
}
@Override public int doHash(Object o) {
return o.hashCode();
}
private Object readResolve() {
return INSTANCE;
}
private static final long serialVersionUID = 1;
}
private static final class Identity extends Equivalence<Object>
implements Serializable {
static final Identity INSTANCE = new Identity();
@Override protected boolean doEquivalent(Object a, Object b) {
return false;
}
@Override protected int doHash(Object o) {
return System.identityHashCode(o);
}
private Object readResolve() {
return INSTANCE;
}
private static final long serialVersionUID = 1;
}
}
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