/* |
|
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. |
|
* |
|
* This code is free software; you can redistribute it and/or modify it |
|
* under the terms of the GNU General Public License version 2 only, as |
|
* published by the Free Software Foundation. Oracle designates this |
|
* particular file as subject to the "Classpath" exception as provided |
|
* by Oracle in the LICENSE file that accompanied this code. |
|
* |
|
* This code is distributed in the hope that it will be useful, but WITHOUT |
|
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or |
|
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License |
|
* version 2 for more details (a copy is included in the LICENSE file that |
|
* accompanied this code). |
|
* |
|
* You should have received a copy of the GNU General Public License version |
|
* 2 along with this work; if not, write to the Free Software Foundation, |
|
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. |
|
* |
|
* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA |
|
* or visit www.oracle.com if you need additional information or have any |
|
* questions. |
|
*/ |
|
/* |
|
* This file is available under and governed by the GNU General Public |
|
* License version 2 only, as published by the Free Software Foundation. |
|
* However, the following notice accompanied the original version of this |
|
* file: |
|
* |
|
* Written by Doug Lea with assistance from members of JCP JSR-166 |
|
* Expert Group and released to the public domain, as explained at |
|
* http://creativecommons.org/publicdomain/zero/1.0/ |
|
*/ |
|
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 |
|
* {@link Collection#iterator}. 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}/../technotes/guides/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() { |
|
} |
|
/** |
|
* Inserts the specified element into this queue if it is possible to do so |
|
* immediately without violating capacity restrictions, returning |
|
* <tt>true</tt> upon success and throwing an <tt>IllegalStateException</tt> |
|
* if no space is currently available. |
|
* |
|
* <p>This implementation returns <tt>true</tt> if <tt>offer</tt> succeeds, |
|
* else throws an <tt>IllegalStateException</tt>. |
|
* |
|
* @param e the element to add |
|
* @return <tt>true</tt> (as specified by {@link Collection#add}) |
|
* @throws IllegalStateException if the element cannot be added at this |
|
* time due to capacity restrictions |
|
* @throws ClassCastException if the class of the specified element |
|
* prevents it from being added to this queue |
|
* @throws NullPointerException if the specified element is null and |
|
* this queue does not permit null elements |
|
* @throws IllegalArgumentException if some property of this element |
|
* prevents it from being added to this queue |
|
*/ |
|
public boolean add(E e) { |
|
if (offer(e)) |
|
return true; |
|
else |
|
throw new IllegalStateException("Queue full"); |
|
} |
|
/** |
|
* Retrieves and removes the head of this queue. This method differs |
|
* from {@link #poll poll} only in that it throws an exception if this |
|
* queue is empty. |
|
* |
|
* <p>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 method |
|
* differs from {@link #peek peek} only in that it throws an exception if |
|
* this queue is empty. |
|
* |
|
* <p>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 queue. |
|
* The queue 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 |
|
* queue, 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 containing elements to be added to this queue |
|
* @return <tt>true</tt> if this queue changed as a result of the call |
|
* @throws ClassCastException if the class of an element of the specified |
|
* collection prevents it from being added to this queue |
|
* @throws NullPointerException if the specified collection contains a |
|
* null element and this queue does not permit null elements, |
|
* or if the specified collection is null |
|
* @throws IllegalArgumentException if some property of an element of the |
|
* specified collection prevents it from being added to this |
|
* queue, or if the specified collection is this queue |
|
* @throws IllegalStateException if not all the elements can be added at |
|
* this time due to insertion restrictions |
|
* @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; |
|
for (E e : c) |
|
if (add(e)) |
|
modified = true; |
|
return modified; |
|
} |
|
} |