Help:A question about stack

Question

Hi, I met a weird problem,
try {
Stack stack=new Stack();
stack.push(a);
stack.push(b); //a,b are Objects
while(stack.peek() instanceOf Objects)
stack.pop;
System.out.println("Done")
}catch(Exception e) {
System.out.println("Error");
It could be worked, however, I always got the error message, which is so weird.
Can anyboy tell me the reason? Thanks a lot!
Iris

Answer 1

Try the following program:
import java.util.Stack;
public class StackTry
     public static void main(String args[])
          try
               Stack stack=new Stack();
               Integer a  = new Integer(10), b = new Integer(11);
               stack.push(a);
               stack.push(b); //a,b are Objects
               while(stack.peek() instanceof Object)
                    System.out.println(stack.pop());
               System.out.println("Done");
          }catch(Exception e)
               e.printStackTrace();
               System.out.println("Error");
}The problem is when u are doing stack.peek()
After all the elements in stack are poped, stack.peek() is done in the while loop which causes exception to occur. Hence the Error message.
Put a condition to check whether the stack is empty before peeking into the stack.
This should help, i guess.
Manish.