// Stack implemented as array, with exceptions.

class MyPopEmptyStack extends Exception {}
class MyOverflowStack extends Exception {}

public class ArrayStack<T> {
     private T[] stack;
     private int numElements = 0; // points to slot after top element

     public ArrayStack(T[] s) { stack = s; }  

     public boolean emptyStack() { 
         return numElements == 0; }
   
     public T  top() {
         return stack[numElements-1];
       }

     public void push(T X) throws MyOverflowStack {
         if (numElements >= stack.length) throw new MyOverflowStack();
         stack[numElements] = X;
         numElements++;
       }
  
     public T pop() throws MyPopEmptyStack {
         numElements--;
         if (numElements < 0) throw new MyPopEmptyStack();
         return stack[numElements];
      }
}