org.apache.mahout.common.Pair.java Source code

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Here is the source code for org.apache.mahout.common.Pair.java

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/**
 * 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.mahout.common;

import java.io.Serializable;

/** A simple (ordered) pair of two objects. Elements may be null. */
public final class Pair<A, B> implements Comparable<Pair<A, B>>, Serializable {

    private final A first;
    private final B second;

    public Pair(A first, B second) {
        this.first = first;
        this.second = second;
    }

    public A getFirst() {
        return first;
    }

    public B getSecond() {
        return second;
    }

    public Pair<B, A> swap() {
        return new Pair<>(second, first);
    }

    public static <A, B> Pair<A, B> of(A a, B b) {
        return new Pair<>(a, b);
    }

    @Override
    public boolean equals(Object obj) {
        if (!(obj instanceof Pair<?, ?>)) {
            return false;
        }
        Pair<?, ?> otherPair = (Pair<?, ?>) obj;
        return isEqualOrNulls(first, otherPair.getFirst()) && isEqualOrNulls(second, otherPair.getSecond());
    }

    private static boolean isEqualOrNulls(Object obj1, Object obj2) {
        return obj1 == null ? obj2 == null : obj1.equals(obj2);
    }

    @Override
    public int hashCode() {
        int firstHash = hashCodeNull(first);
        // Flip top and bottom 16 bits; this makes the hash function probably different
        // for (a,b) versus (b,a)
        return (firstHash >>> 16 | firstHash << 16) ^ hashCodeNull(second);
    }

    private static int hashCodeNull(Object obj) {
        return obj == null ? 0 : obj.hashCode();
    }

    @Override
    public String toString() {
        return '(' + String.valueOf(first) + ',' + second + ')';
    }

    /**
     * Defines an ordering on pairs that sorts by first value's natural ordering, ascending,
     * and then by second value's natural ordering.
     *
     * @throws ClassCastException if types are not actually {@link Comparable}
     */
    @Override
    public int compareTo(Pair<A, B> other) {
        Comparable<A> thisFirst = (Comparable<A>) first;
        A thatFirst = other.getFirst();
        int compare = thisFirst.compareTo(thatFirst);
        if (compare != 0) {
            return compare;
        }
        Comparable<B> thisSecond = (Comparable<B>) second;
        B thatSecond = other.getSecond();
        return thisSecond.compareTo(thatSecond);
    }

}