/*
 * [The "BSD license"]
 *  Copyright (c) 2012 Terence Parr
 *  Copyright (c) 2012 Sam Harwell
 *  All rights reserved.
 *
 *  Redistribution and use in source and binary forms, with or without
 *  modification, are permitted provided that the following conditions
 *  are met:
 *
 *  1. Redistributions of source code must retain the above copyright
 *     notice, this list of conditions and the following disclaimer.
 *  2. Redistributions in binary form must reproduce the above copyright
 *     notice, this list of conditions and the following disclaimer in the
 *     documentation and/or other materials provided with the distribution.
 *  3. The name of the author may not be used to endorse or promote products
 *     derived from this software without specific prior written permission.
 *
 *  THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 *  IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 *  OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 *  IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
 *  INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 *  NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 *  DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 *  THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 *  (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 *  THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */
package org.antlr.v4.runtime.misc;

/**
 * This default implementation of {@link EqualityComparator} uses object equality
 * for comparisons by calling {@link Object#hashCode} and {@link Object#equals}.
 *
 * @author Sam Harwell
 */
public final class ObjectEqualityComparator extends AbstractEqualityComparator<Object> {
	public static final ObjectEqualityComparator INSTANCE = new ObjectEqualityComparator();

	/**
	 * {@inheritDoc}
	 *
	 * <p>This implementation returns
	 * {@code obj.}{@link Object#hashCode hashCode()}.</p>
	 */
	@Override
	public int hashCode(Object obj) {
		if (obj == null) {
			return 0;
		}

		return obj.hashCode();
	}

	/**
	 * {@inheritDoc}
	 *
	 * <p>This implementation relies on object equality. If both objects are
	 * {@code null}, this method returns {@code true}. Otherwise if only
	 * {@code a} is {@code null}, this method returns {@code false}. Otherwise,
	 * this method returns the result of
	 * {@code a.}{@link Object#equals equals}{@code (b)}.</p>
	 */
	@Override
	public boolean equals(Object a, Object b) {
		if (a == null) {
			return b == null;
		}

		return a.equals(b);
	}

}