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Java example source code file (Pair.java)

This example Java source code file (Pair.java) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

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Java - Java tags/keywords

override, pair, string

The Pair.java Java example source code

/*
 * 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.math3.util;

/**
 * Generic pair.
 * <br/>
 * Although the instances of this class are immutable, it is impossible
 * to ensure that the references passed to the constructor will not be
 * modified by the caller.
 *
 * @param <K> Key type.
 * @param <V> Value type.
 *
 * @since 3.0
 */
public class Pair<K, V> {
    /** Key. */
    private final K key;
    /** Value. */
    private final V value;

    /**
     * Create an entry representing a mapping from the specified key to the
     * specified value.
     *
     * @param k Key (first element of the pair).
     * @param v Value (second element of the pair).
     */
    public Pair(K k, V v) {
        key = k;
        value = v;
    }

    /**
     * Create an entry representing the same mapping as the specified entry.
     *
     * @param entry Entry to copy.
     */
    public Pair(Pair<? extends K, ? extends V> entry) {
        this(entry.getKey(), entry.getValue());
    }

    /**
     * Get the key.
     *
     * @return the key (first element of the pair).
     */
    public K getKey() {
        return key;
    }

    /**
     * Get the value.
     *
     * @return the value (second element of the pair).
     */
    public V getValue() {
        return value;
    }

    /**
     * Get the first element of the pair.
     *
     * @return the first element of the pair.
     * @since 3.1
     */
    public K getFirst() {
        return key;
    }

    /**
     * Get the second element of the pair.
     *
     * @return the second element of the pair.
     * @since 3.1
     */
    public V getSecond() {
        return value;
    }

    /**
     * Compare the specified object with this entry for equality.
     *
     * @param o Object.
     * @return {@code true} if the given object is also a map entry and
     * the two entries represent the same mapping.
     */
    @Override
    public boolean equals(Object o) {
        if (this == o) {
            return true;
        }
        if (!(o instanceof Pair)) {
            return false;
        } else {
            Pair<?, ?> oP = (Pair) o;
            return (key == null ?
                    oP.key == null :
                    key.equals(oP.key)) &&
                (value == null ?
                 oP.value == null :
                 value.equals(oP.value));
        }
    }

    /**
     * Compute a hash code.
     *
     * @return the hash code value.
     */
    @Override
    public int hashCode() {
        int result = key == null ? 0 : key.hashCode();

        final int h = value == null ? 0 : value.hashCode();
        result = 37 * result + h ^ (h >>> 16);

        return result;
    }

    /** {@inheritDoc} */
    @Override
    public String toString() {
        return "[" + getKey() + ", " + getValue() + "]";
    }

    /**
     * Convenience factory method that calls the
     * {@link #Pair(Object, Object) constructor}.
     *
     * @param <K> the key type
     * @param <V> the value type
     * @param k First element of the pair.
     * @param v Second element of the pair.
     * @return a new {@code Pair} containing {@code k} and {@code v}.
     * @since 3.3
     */
    public static <K, V> Pair create(K k, V v) {
        return new Pair<K, V>(k, v);
    }
}

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