- /*
- * @(#)AbstractQueue.java 1.6 04/01/27
- *
- * Copyright 2004 Sun Microsystems, Inc. All rights reserved.
- * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
- */
-
- package java.util;
-
- /**
- * This class provides skeletal implementations of some {@link Queue}
- * operations. The implementations in this class are appropriate when
- * the base implementation does <em>not</em> allow <tt>null</tt>
- * elements. Methods {@link #add add}, {@link #remove remove}, and
- * {@link #element element} are based on {@link #offer offer}, {@link
- * #poll poll}, and {@link #peek peek}, respectively but throw
- * exceptions instead of indicating failure via <tt>false</tt> or
- * <tt>null</tt> returns.
- *
- * <p> A <tt>Queue</tt> implementation that extends this class must
- * minimally define a method {@link Queue#offer} which does not permit
- * insertion of <tt>null</tt> elements, along with methods {@link
- * Queue#peek}, {@link Queue#poll}, {@link Collection#size}, and a
- * {@link Collection#iterator} supporting {@link
- * Iterator#remove}. Typically, additional methods will be overridden
- * as well. If these requirements cannot be met, consider instead
- * subclassing {@link AbstractCollection}.
- *
- * <p>This class is a member of the
- * <a href="{@docRoot}/../guide/collections/index.html">
- * Java Collections Framework</a>.
- *
- * @since 1.5
- * @author Doug Lea
- * @param <E> the type of elements held in this collection
- */
- public abstract class AbstractQueue<E>
- extends AbstractCollection<E>
- implements Queue<E> {
-
- /**
- * Constructor for use by subclasses.
- */
- protected AbstractQueue() {
- }
-
-
- /**
- * Adds the specified element to this queue. This implementation
- * returns <tt>true</tt> if <tt>offer</tt> succeeds, else
- * throws an IllegalStateException.
- *
- * @param o the element
- * @return <tt>true</tt> (as per the general contract of
- * <tt>Collection.add</tt>).
- *
- * @throws NullPointerException if the specified element is <tt>null</tt>
- * @throws IllegalStateException if element cannot be added
- */
- public boolean add(E o) {
- if (offer(o))
- return true;
- else
- throw new IllegalStateException("Queue full");
- }
-
- /**
- * Retrieves and removes the head of this queue.
- * This implementation returns the result of <tt>poll</tt>
- * unless the queue is empty.
- *
- * @return the head of this queue.
- * @throws NoSuchElementException if this queue is empty.
- */
- public E remove() {
- E x = poll();
- if (x != null)
- return x;
- else
- throw new NoSuchElementException();
- }
-
-
- /**
- * Retrieves, but does not remove, the head of this queue.
- * This implementation returns the result of <tt>peek</tt>
- * unless the queue is empty.
- *
- * @return the head of this queue.
- * @throws NoSuchElementException if this queue is empty.
- */
- public E element() {
- E x = peek();
- if (x != null)
- return x;
- else
- throw new NoSuchElementException();
- }
-
- /**
- * Removes all of the elements from this collection.
- * The collection will be empty after this call returns.
- * <p>This implementation repeatedly invokes {@link #poll poll} until it
- * returns <tt>null</tt>.
- */
- public void clear() {
- while (poll() != null)
- ;
- }
-
- /**
- * Adds all of the elements in the specified collection to this
- * queue. Attempts to addAll of a queue to itself result in
- * <tt>IllegalArgumentException</tt>. Further, the behavior of
- * this operation is undefined if the specified collection is
- * modified while the operation is in progress.
- *
- * <p>This implementation iterates over the specified collection,
- * and adds each element returned by the iterator to this
- * collection, in turn. A runtime exception encountered while
- * trying to add an element (including, in particular, a
- * <tt>null</tt> element) may result in only some of the elements
- * having been successfully added when the associated exception is
- * thrown.
- *
- * @param c collection whose elements are to be added to this collection.
- * @return <tt>true</tt> if this collection changed as a result of the
- * call.
- * @throws NullPointerException if the specified collection or
- * any of its elements are null.
- * @throws IllegalArgumentException if c is this queue.
- *
- * @see #add(Object)
- */
- public boolean addAll(Collection<? extends E> c) {
- if (c == null)
- throw new NullPointerException();
- if (c == this)
- throw new IllegalArgumentException();
- boolean modified = false;
- Iterator<? extends E> e = c.iterator();
- while (e.hasNext()) {
- if (add(e.next()))
- modified = true;
- }
- return modified;
- }
-
- }