public class Equal extends Expression {   private Expression firstOp, secondOp;      public Equal(Expression f, Expression s) {      firstOp = (Expression)f.clone();      secondOp = (Expression)s.clone();   }      public int eval() {      return ((firstOp.eval() == secondOp.eval())?1:0);   }      public Object clone() {      return new Equal(firstOp, secondOp);   }      public String toString() {      return firstOp.toString()+secondOp.toString()+labelling()+"EQN\n";   }}