public class ArrayStack<E> {
    
    private int capacity;                   // stack capacity
    public static final int CAPACITY = 100; // default stack capacity
    private E[] S;                          // E array used to implement the stack
    private int tos = -1;                   // index for the top of stack
    
    public ArrayStack(){this(CAPACITY);}
    
    @SuppressWarnings("unchecked")
    public ArrayStack(int cap){
	capacity = cap;
	S = (E[]) new Object [capacity]; 
    }
    
    public int size(){return tos+1;}
    
    public boolean isEmpty(){return tos == -1;}
    
    public void push(E element) throws StackException {
	if (size() == capacity)
	    throw new StackException("Stack overflow");
	tos++;
	S[tos] = element;
    }
    
    public E top() throws StackException{
	if (isEmpty()) throw new StackException("Stack empty");
	return S[tos];
    }
    
    public E pop() throws StackException {
	if (isEmpty()) throw new StackException("Stack underflow");
	E element = S[tos];
	S[tos] = null;
	tos--;		
	return element;
    }
    
    public String toString(){
	String s = "[";
	if (tos >= 0) s = s + S[0];
	for (int i=1;i<=tos;i++) s = s +","+ S[i];
	return s + "]";
    }
}