org.aspectj/docs/examples/introduction/HashablePoint.java

/*
Copyright (c) Xerox Corporation 1998-2002.  All rights reserved.

Use and copying of this software and preparation of derivative works based
upon this software are permitted.  Any distribution of this software or
derivative works must comply with all applicable United States export control
laws.

This software is made available AS IS, and Xerox Corporation makes no warranty
about the software, its performance or its conformity to any specification.
*/

package introduction;

import java.util.Hashtable;

public aspect HashablePoint {

   public int Point.hashCode() {
      return (int) (getX() + getY() % Integer.MAX_VALUE);
   }

   public boolean Point.equals(Object o) {
      if (o == this) { return true; }
      if (!(o instanceof Point)) { return false; }
      Point other = (Point)o;
      return (getX() == other.getX()) && (getY() == other.getY());
   }

   public static void main(String[] args) {
      Hashtable h = new Hashtable();
      Point p1 = new Point();

      p1.setRectangular(10, 10);
      Point p2 = new Point();

      p2.setRectangular(10, 10);

      System.out.println("p1 = " + p1);
      System.out.println("p2 = " + p2);
      System.out.println("p1.hashCode() = " + p1.hashCode());
      System.out.println("p2.hashCode() = " + p2.hashCode());

      h.put(p1, "P1");
      System.out.println("Got: " + h.get(p2));
   }
}