Pair.java

/*
 * Copyright (C) 2017 Daniel Gallego Vico.
 *
 * 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.
 */

import java.util.Objects;

/**
 * Container to ease passing around a tuple of two objects.
 * This object provides a sensible implementation of equals(),
 * returning true if equals() is true on each of the contained objects.
 *
 * @param <F> First object type to store in the {@link Pair}
 * @param <S> Second object type to store in the {@link Pair}
 */
public class Pair<F, S> {
    public final F first;
    public final S second;

    /**
     * Constructor.
     *
     * @param first The first object in the {@link Pair}
     * @param second The second object in the {@link Pair}
     */
    public Pair(F first, S second) {
        this.first = first;
        this.second = second;
    }

    /**
     * Checks the two {@link Pair} objects for equality by delegating to their respective
     * {@link Object#equals(Object)} methods.
     *
     * @param o The {@link Pair} to which this one is to be checked for equality
     * @return true if the underlying objects of the {@link Pair} are considered equal
     */
    @Override
    public boolean equals(Object o) {
        if(!(o instanceof Pair)) {
            return false;
        }
        Pair<?,?> p = (Pair<?,?>) o;
        return Objects.equals(p.first, first)
                && Objects.equals(p.second, second);
    }

    /**
     * Compute a hash code using the hash codes of the underlying objects.
     *
     * @return a hashcode on the {@link Pair}
     */
    @Override
    public int hashCode() {
        return (first == null ? 0 : first.hashCode())
                ^ (second == null ? 0 : second.hashCode());
    }

    /**
     * Convenience method for creating an appropriately typed {@link Pair}.
     *
     * @param a The first object in the {@link Pair}
     * @param b The second object in the {@link Pair}
     * @param <A> First object type of the {@link Pair}
     * @param <B> Second object type of the {@link Pair}
     *           
     * @return a {@link Pair} that is templatized with the types of a and b
     */
    public static <A, B> Pair<A, B> create(A a, B b) {
        return new Pair<>(a, b);
    }
  
}