| /******************************************************************************* |
| * Copyright (c) 2015 Oracle. All rights reserved. |
| * This program and the accompanying materials are made available under the |
| * terms of the Eclipse Public License 2.0, which accompanies this distribution |
| * and is available at https://www.eclipse.org/legal/epl-2.0/. |
| * |
| * Contributors: |
| * Oracle - initial API and implementation |
| ******************************************************************************/ |
| package org.eclipse.jpt.common.utility.internal.deque; |
| |
| import java.io.Serializable; |
| import java.util.NoSuchElementException; |
| import org.eclipse.jpt.common.utility.deque.Deque; |
| |
| /** |
| * Empty implementation of the {@link Deque} interface. |
| * @param <E> the type of elements maintained by the deque |
| * @see DequeTools |
| */ |
| public final class EmptyDeque<E> |
| implements Deque<E>, Serializable |
| { |
| @SuppressWarnings("rawtypes") |
| public static final Deque INSTANCE = new EmptyDeque(); |
| @SuppressWarnings("unchecked") |
| public static <E> Deque<E> instance() { |
| return INSTANCE; |
| } |
| |
| // ensure single instance |
| private EmptyDeque() { |
| super(); |
| } |
| |
| public void enqueueTail(E o) { |
| throw new UnsupportedOperationException(); |
| } |
| |
| public void enqueueHead(E o) { |
| throw new UnsupportedOperationException(); |
| } |
| |
| public E dequeueHead() { |
| throw new NoSuchElementException(); |
| } |
| |
| public E dequeueTail() { |
| throw new NoSuchElementException(); |
| } |
| |
| public E peekHead() { |
| throw new NoSuchElementException(); |
| } |
| |
| public E peekTail() { |
| throw new NoSuchElementException(); |
| } |
| |
| public boolean isEmpty() { |
| return true; |
| } |
| |
| @Override |
| public String toString() { |
| return "[]"; //$NON-NLS-1$ |
| } |
| |
| private static final long serialVersionUID = 1L; |
| private Object readResolve() { |
| // replace this object with the singleton |
| return INSTANCE; |
| } |
| } |