| /******************************************************************************* |
| * Copyright (c) 2007, 2010 Oracle. All rights reserved. |
| * This program and the accompanying materials are made available under the |
| * terms of the Eclipse Public License v1.0, which accompanies this distribution |
| * and is available at http://www.eclipse.org/legal/epl-v10.html. |
| * |
| * Contributors: |
| * Oracle - initial API and implementation |
| ******************************************************************************/ |
| package org.eclipse.jpt.utility.internal; |
| |
| import java.io.Serializable; |
| import java.util.EmptyStackException; |
| |
| /** |
| * Interface defining the classic stack behavior, |
| * without the backdoors allowed by {@link java.util.Stack}. |
| * |
| * @param <E> the type of elements contained by the stack |
| */ |
| public interface Stack<E> { |
| |
| /** |
| * "Push" the specified item on to the top of the stack. |
| */ |
| void push(E element); |
| |
| /** |
| * "Pop" an item from the top of the stack. |
| */ |
| E pop(); |
| |
| /** |
| * Return the item on the top of the stack |
| * without removing it from the stack. |
| */ |
| E peek(); |
| |
| /** |
| * Return whether the stack is empty. |
| */ |
| boolean isEmpty(); |
| |
| |
| final class Empty<E> implements Stack<E>, Serializable { |
| @SuppressWarnings("rawtypes") |
| public static final Stack INSTANCE = new Empty(); |
| @SuppressWarnings("unchecked") |
| public static <T> Stack<T> instance() { |
| return INSTANCE; |
| } |
| // ensure single instance |
| private Empty() { |
| super(); |
| } |
| public void push(E element) { |
| throw new UnsupportedOperationException(); |
| } |
| public E pop() { |
| throw new EmptyStackException(); |
| } |
| public E peek() { |
| throw new EmptyStackException(); |
| } |
| public boolean isEmpty() { |
| return true; |
| } |
| private static final long serialVersionUID = 1L; |
| private Object readResolve() { |
| // replace this object with the singleton |
| return INSTANCE; |
| } |
| } |
| |
| } |