//************************************************************************
//	Mark Allen Weiss
//	
//  Stack.java
//  Copy from StackAr.java by Mark Allen Weiss
// ***********************************************************************


class Stack {

	private Object [] theArray;
	private int topOfStack;

	private static int DEFAULT_CAPACITY = 64;
	/*
	* Construct the stack.
	*/
	public Stack()
	{
		this( DEFAULT_CAPACITY );
	}

	/**
	* Construct the stack.
	* @param capacity the capacity.
	*/
	public Stack( int capacity )
	{
		theArray = new Object[ capacity ];
		topOfStack = -1;
	}

	/**
	* Test if the stack is logically empty.
	* @return true if empty, false otherwise.
	*/
	public boolean isEmpty( )
	{
		return topOfStack == -1;
	}

	/**
	* Test if the stack is logically full.
	* @return true if full, false otherwise.
	*/
	public boolean isFull( )
	{
	return topOfStack == theArray.length - 1;
	}

	/**
	* Make the stack logically empty.
	*/
	public void makeEmpty( )
	{
	topOfStack = -1;
	}

	/**
	* Get the most recently inserted item in the stack.
	* Does not alter the stack.
	* @return the most recently inserted item in the stack, or null, if empty.
	*/
	public Object top( )
	{
		if( isEmpty( ) )
			return null;
		return theArray[ topOfStack ];
	}

	/**
	* Remove the most recently inserted item from the stack.
	* @exception Underflow if stack is already empty.
	*/
	public void pop( ) throws Underflow
	{
		if( isEmpty( ) )
			throw new Underflow( );
		theArray[ topOfStack-- ] = null;
	}

	/**
	* Insert a new item into the stack, if not already full.
	* @param x the item to insert.
	* @exception Overflow if stack is already full.
	*/
	public void push( Object x ) throws Overflow
	{
		if( isFull( ) )
			throw new Overflow( );
		theArray[ ++topOfStack ] = x;
	}

	/**
	* Return and remove most recently inserted item from the stack.
	* @return most recently inserted item, or null, if stack is empty.
	*/
	public Object topAndPop( )
	{
		if( isEmpty( ) )
			return null;
		Object topItem = top( );
		theArray[ topOfStack-- ] = null;
		return topItem;
	}
	/**
	* Displays stack.
	*/
	public void dispStack() throws Underflow {
		while (!isEmpty()) {
			System.out.println(top());
		}
	} // end dump


}