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Collections and collection utilities for Neo4j.
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/*
 * Copyright (c) "Neo4j"
 * Neo4j Sweden AB [http://neo4j.com]
 *
 * This file is part of Neo4j.
 *
 * Neo4j is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see .
 */
package org.neo4j.internal.helpers.collection;

import java.util.Objects;

/**
 * Utility to handle pairs of objects.
 *
 * @param  the type of the {@link #first() first value} of the pair.
 * @param  the type of the {@link #other() other value} of the pair.
 */
public abstract class Pair
{
    /**
     * Create a new pair of objects.
     *
     * @param first the first object in the pair.
     * @param other the other object in the pair.
     * @param  the type of the first object in the pair
     * @param  the type of the second object in the pair
     * @return a new pair of the two parameters.
     */
    public static  Pair pair( final T1 first, final T2 other )
    {
        return new Pair<>()
        {
            @Override
            public T1 first()
            {
                return first;
            }

            @Override
            public T2 other()
            {
                return other;
            }
        };
    }

    /**
     * Alias of {@link #pair(Object, Object)}.
     * @param first the first object in the pair.
     * @param other the other object in the pair.
     * @param  the type of the first object in the pair
     * @param  the type of the second object in the pair
     * @return a new pair of the two parameters.
     */
    public static  Pair of( final T1 first, final T2 other )
    {
        return pair( first, other );
    }

    Pair()
    {
        // package private, limited number of subclasses
    }

    /**
     * @return the first object in the pair.
     */
    public abstract T1 first();

    /**
     * @return the other object in the pair.
     */
    public abstract T2 other();

    @Override
    public String toString()
    {
        return "(" + first() + ", " + other() + ")";
    }

    @Override
    public int hashCode()
    {
        return ( 31 * hashCode( first() ) ) | hashCode( other() );
    }

    @Override
    public boolean equals( Object obj )
    {
        if ( this == obj )
        {
            return true;
        }
        if ( obj instanceof Pair )
        {
            Pair that = (Pair) obj;
            return Objects.equals( this.other(), that.other() ) && Objects.equals( this.first(), that.first() );
        }
        return false;
    }

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