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

    // Constants

    private static final int MIN_CAPACITY = 100;
    private static final double GROWTH_FACTOR = 1.5;

    // Instance variables

    private E[] elems;
    private int top = -1; // designates the top element or -1 if empty

    @SuppressWarnings( "unchecked" )

    public DynamicArrayStack() {
        // pre-condictions: 
        elems = (E[]) new Object[ MIN_CAPACITY ];
    }

    // Returns true if this stack is empty;
    public boolean isEmpty() {
        return top == -1;
    }

    // Returns the top element of this stack without removing it.
    public E peek() {
        // pre-conditions: ! isEmpty()
        return elems[ top ];
    }

    // Returns and remove the top element of this stack.
    public E pop() {
        // pre-conditions: ! isEmpty()

        // save the top element
        E saved = elems[ top ];

        // scrub the memory, then decrements top
        elems[ top-- ] = null; 

        return saved;
    }

    // Puts the element onto the top of this stack.
    public void push( E element ) {
        if ( top == ( elems.length - 1 ) ) {
            increaseSize();
        }
        // increments top, stores the element at position top
        elems[ ++top ] = element;
    }

    @SuppressWarnings( "unchecked" )

    private void increaseSize() {
        E[] newElems;

        int newSize = (int) ( elems.length * GROWTH_FACTOR );   

        newElems = (E[]) new Object[ newSize ];
        System.arraycopy( elems, 0, newElems, 0, elems.length );

        // Replacing elems with the new/larger array
        elems = newElems;
    }

}