com.google.common.base.Pair.java Source code

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/* Copyright (c) 2008 Google Inc.
 *
 * 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 java.io.*;

/**
 * Pair is an expedient way to combine two arbitrary objects into one.  <b>Its
 * use is not to be preferred</b> to creating a custom type, but it can be
 * handy in a pinch.  If your {@link #equals}, {@link #hashCode},
 * {@link #toString}, and/or {@link #clone} behavior matter to you at all, you
 * may not want to use this (or you may at least wish to subclass).
 *
 *
    
 *
 * <p>This class may be used with the Google Web Toolkit (GWT).
 *
 */
@SuppressWarnings({ "UnusedDeclaration", "unchecked" })
public class Pair<A, B> implements Serializable, Cloneable {
    private static final long serialVersionUID = 747826592375603043L;

    /** Creates a new pair containing the given objects in order. */
    public static <A, B> Pair<A, B> of(A first, B second) {
        return new Pair<A, B>(first, second);
    }

    /** The first element of the pair. */
    public final A first;

    /** The second element of the pair. */
    public final B second;

    /** Cumbersome way to create a new pair (see {@link #of}. */
    public Pair(A first, B second) {
        this.first = first;
        this.second = second;
    }

    /** Optional accessor method for {@link #first}. */
    public A getFirst() {
        return first;
    }

    /** Optional accessor method for {@link #second}. */
    public B getSecond() {
        return second;
    }

    @Override
    public Pair<A, B> clone() {
        try {
            return (Pair<A, B>) super.clone();
        } catch (CloneNotSupportedException e) {
            throw new AssertionError(e);

        }
    }

    @Override
    public boolean equals(Object object) {

        if (object instanceof Pair<?, ?>) {
            Pair<?, ?> other = (Pair<?, ?>) object;
            return eq(first, other.first) && eq(second, other.second);
        }
        return false;
    }

    @Override
    public int hashCode() {
        /*
         * This combination yields entropy comparable to constituent hashes
         * and ensures that hash(a,b) != hash(b,a).
         */
        return (hash(first, 0) + 0xDeadBeef) ^ hash(second, 0);
    }

    /**
     * This implementation returns the String representation of this pair in
     * the form {@code (string1, string2)}, where {@code string1} and
     * {@code string2} are the {@link Object#toString} representations of the
     * elements inside the pair.
     */
    @Override
    public String toString() {
        return String.format("(%s, %s)", first, second);
    }

    private static boolean eq(Object a, Object b) {
        return a == b || (a != null && a.equals(b));
    }

    private static int hash(Object object, int nullHash) {
        return (object == null) ? nullHash : object.hashCode();
    }
}