//http://www.moviemalls.com/M/memento.htm

/**
 * This does the computations and furnishes and uses Mementos for undoes.
 * <br>Memento Design Pattern example for COM1204 Summer 2003.
 *
 * @author Bob Futrelle
 * @version 0.1, 4 July 2003
 *
 */
 
 public class Engine {
 	
	private int result; // initially zero
	
	int getResult() {
		return result;
	}
	void postResult(){
		System.out.println("Result now = " + result);
	}
	void times(int factor) {
		result *= factor;
		postResult();
	}
	void add(int summand) {
		result += summand;
		postResult();
	}
	Memento getMemo() {
		return new Memento();
	}
	void reset(Object m) {
		result = ((Memento)m).savedResult;
	} // reset
	
	// Here's the trick, a private class only Engine can produce and use.
	private class Memento {
			private int savedResult;
			private Memento() {
				savedResult = result;
			}
	}
	
 } // class Engine