/*
 * @(#)StackImpl.java	1.11 04/06/21
 *
 * Copyright 2004 Sun Microsystems, Inc. All rights reserved.
 * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 */

package com.sun.corba.se.impl.orbutil ;

import java.util.EmptyStackException ;

// We implement a Stack here instead of using java.util.Stack because
// java.util.Stack is thread-safe, negatively impacting performance.
// We use an ArrayList instead since it is not thread-safe.  
// RequestInfoStack is used quite frequently.
public class StackImpl {
    // The stack for RequestInfo objects.  
    private Object[] data = new Object[3] ;
    private int top = -1 ;

    // Tests if this stack is empty.
    public final boolean empty() {
	return top == -1;
    }

    // Looks at the object at the top of this stack without removing it
    // from the stack.
    public final Object peek() {
	if (empty()) 
	    throw new EmptyStackException();

	return data[ top ];
    }

    // Removes the object at the top of this stack and returns that 
    // object as the value of this function.
    public final Object pop() {
	Object obj = peek() ;
	data[top] = null ;
	top-- ;
	return obj;
    }

    private void ensure() 
    {
	if (top == (data.length-1)) {
	    int newSize = 2*data.length ;
	    Object[] newData = new Object[ newSize ] ;
	    System.arraycopy( data, 0, newData, 0, data.length ) ;
	    data = newData ;
	}
    }

    // Pushes an item onto the top of the stack
    public final Object push( Object item ) {
	ensure() ;
	top++ ;
	data[top] = item;
	return item;
    }
}