gistfile1.java

class Y extends X {
  public boolean equals (Object other) {
    if (other == null || !(other instanceof Y)) {
      return false;
    }

    Y y = (Y) other;

    return x == y.x;
  }
}

public class X {
  public int x;

  public static void main (String[] args) {
    X x = new X();
    Y y = new Y();

    x.x = y.x = 5;

    System.out.println(x.equals(y));
    System.out.println(y.equals(x));
  }

  public boolean equals (Object other) {
    try {
      return this.x == ((X) other).x;
    } catch (Exception e) {
      return false;
    }
  }
}