/*
* Copyright 2007 Google Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License"); you may not
* use this file except in compliance with the License. You may obtain a copy of
* the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
* License for the specific language governing permissions and limitations under
* the License.
*/
package java.util;
/**
* Skeletal implementation of the Queue interface. <a
* href="http://java.sun.com/j2se/1.5.0/docs/api/java/util/AbstractQueue.html">[Sun
* docs]</a>
*
* @param <E> element type.
*/
public abstract class AbstractQueue<E> extends AbstractCollection<E> implements
Queue<E> {
// Should not be instantiated directly.
protected AbstractQueue() {
}
@Override
public boolean add(E o) {
if (offer(o)) {
return true;
}
throw new IllegalStateException("Unable to add element to queue");
}
@Override
public boolean addAll(Collection<? extends E> c) {
if (c == this) {
throw new IllegalArgumentException("Can't add a queue to itself");
}
boolean modified = false;
for (E val : c) {
modified |= add(val);
}
return modified;
}
@Override
public void clear() {
while (poll() != null) {
// empty loop
}
}
public E element() {
E e = peek();
if (e == null) {
throw new NoSuchElementException("Queue is empty");
}
return e;
}
public abstract boolean offer(E o);
public abstract E peek();
public abstract E poll();
public E remove() {
E e = poll();
if (e == null) {
throw new NoSuchElementException("Queue is empty");
}
return e;
}
}