/*
 * dk.brics.automaton
 * 
 * Copyright (c) 2001-2011 Anders Moeller
 * 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 dk.brics.automaton;

/**
 * Pair of states.
 * @author Anders M&oslash;ller &lt;<a href="mailto:amoeller@cs.au.dk">amoeller@cs.au.dk</a>&gt;
 */
public class StatePair {
	State s;
	State s1;
	State s2;
	
	StatePair(State s, State s1, State s2) {
		this.s = s;
		this.s1 = s1;
		this.s2 = s2;
	}
	
	/**
	 * Constructs a new state pair.
	 * @param s1 first state
	 * @param s2 second state
	 */
	public StatePair(State s1, State s2) {
		this.s1 = s1;
		this.s2 = s2;
	}
	
	/**
	 * Returns first component of this pair.
	 * @return first state
	 */
	public State getFirstState() {
		return s1;
	}
	
	/**
	 * Returns second component of this pair.
	 * @return second state
	 */
	public State getSecondState() {
		return s2;
	}
	
	/** 
	 * Checks for equality.
	 * @param obj object to compare with
	 * @return true if <tt>obj</tt> represents the same pair of states as this pair
	 */
	@Override
	public boolean equals(Object obj) {
		if (obj instanceof StatePair) {
			StatePair p = (StatePair)obj;
			return p.s1 == s1 && p.s2 == s2;
		}
		else
			return false;
	}
	
	/** 
	 * Returns hash code.
	 * @return hash code
	 */
	@Override
	public int hashCode() {
		return s1.hashCode() + s2.hashCode();
	}
}
