//stack implementation using array
//Author: Konstantin Voevodski
//Date: 6/4/07


public class myArrayStack<AnyType>
{
   private static final int DEFAULT_CAPACITY = 10;
   private int size;
   private AnyType[] items;
 
    //constructor just creates an empty stack
    public myArrayStack () 
    {
	size = 0;
        items = (AnyType[]) new Object[DEFAULT_CAPACITY];
    }

    public boolean isEmpty () 
    {
	return (size == 0);
    }


    //insert item in the back of the array, increase size of array if necessary
    public void push (AnyType value) 
    {
            if(items.length == size)
            {
                  ensureCapacity(size * 2 + 1);
            }
	    items[size++] = value;
            //note the postfix use of the ++ operator, it is incremented AFTER it is used
    }

    //remove item from the back of the array
    public AnyType pop () 
    {
        if(isEmpty())
        {
             throw new java.util.NoSuchElementException();
        }
	return(items[--size]);
        //note the prefix use of the ++ operator, it is incremented BEFORE it is used
    }

    public void ensureCapacity(int newCapacity)
    //increase the size of the array
    {
        AnyType[] old = items;
        items = (AnyType[]) new Object[newCapacity];
        //create a new array to hold the items and copy them over
        for(int x = 0; x < size; x++)
        {
            items[x] = old[x];
        }
    }
}