public class ArrayStack<E> implements Stack<E> {

    // Instance variables
    
    private E[] elems;
    private int top;

    // Constructor
    
    public ArrayStack( int capacity ) {
        elems = (E[]) new Object[ capacity ];
        top = 0;
    }
    
    public boolean isEmpty() {
        return ( top == 0 );
    }

    
    public E peek() {
        return elems[ top-1 ];
    }

    public E pop() {
        E saved = elems[ --top ];
        elems[ top ] = null; // scrub the memory!
        return saved;
    }

    public void push( E element ) {

	if (top == elems.length) { // increase size
	    E[] newArray;
	    newArray = (E[]) new Object[ elems.length * 2 ];
	    for (int i=0; i<top; i++) {
		newArray[i] = elems[i];
	    }
	    elems = newArray;
	}
	
        elems[ top++ ] = element;
    }
}