193 lines
7.4 KiB
Java
193 lines
7.4 KiB
Java
/*
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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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*
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* This code is free software; you can redistribute it and/or modify it
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* under the terms of the GNU General Public License version 2 only, as
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* published by the Free Software Foundation. Oracle designates this
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* particular file as subject to the "Classpath" exception as provided
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* by Oracle in the LICENSE file that accompanied this code.
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*
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* This code is distributed in the hope that it will be useful, but WITHOUT
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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* version 2 for more details (a copy is included in the LICENSE file that
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* accompanied this code).
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*
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* You should have received a copy of the GNU General Public License version
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* 2 along with this work; if not, write to the Free Software Foundation,
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* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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*
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* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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* or visit www.oracle.com if you need additional information or have any
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* questions.
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*/
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/*
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* This file is available under and governed by the GNU General Public
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* License version 2 only, as published by the Free Software Foundation.
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* However, the following notice accompanied the original version of this
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* file:
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*
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* Written by Doug Lea with assistance from members of JCP JSR-166
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* Expert Group and released to the public domain, as explained at
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* http://creativecommons.org/publicdomain/zero/1.0/
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*/
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package java.util;
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// BEGIN android-note
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// removed link to collections framework docs
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// END android-note
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/**
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* This class provides skeletal implementations of some {@link Queue}
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* operations. The implementations in this class are appropriate when
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* the base implementation does <em>not</em> allow {@code null}
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* elements. Methods {@link #add add}, {@link #remove remove}, and
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* {@link #element element} are based on {@link #offer offer}, {@link
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* #poll poll}, and {@link #peek peek}, respectively, but throw
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* exceptions instead of indicating failure via {@code false} or
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* {@code null} returns.
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*
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* <p>A {@code Queue} implementation that extends this class must
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* minimally define a method {@link Queue#offer} which does not permit
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* insertion of {@code null} elements, along with methods {@link
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* Queue#peek}, {@link Queue#poll}, {@link Collection#size}, and
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* {@link Collection#iterator}. Typically, additional methods will be
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* overridden as well. If these requirements cannot be met, consider
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* instead subclassing {@link AbstractCollection}.
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*
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* @since 1.5
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* @author Doug Lea
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* @param <E> the type of elements held in this queue
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*/
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public abstract class AbstractQueue<E>
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extends AbstractCollection<E>
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implements Queue<E> {
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/**
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* Constructor for use by subclasses.
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*/
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protected AbstractQueue() {
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}
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/**
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* Inserts the specified element into this queue if it is possible to do so
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* immediately without violating capacity restrictions, returning
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* {@code true} upon success and throwing an {@code IllegalStateException}
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* if no space is currently available.
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*
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* <p>This implementation returns {@code true} if {@code offer} succeeds,
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* else throws an {@code IllegalStateException}.
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*
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* @param e the element to add
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* @return {@code true} (as specified by {@link Collection#add})
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* @throws IllegalStateException if the element cannot be added at this
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* time due to capacity restrictions
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* @throws ClassCastException if the class of the specified element
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* prevents it from being added to this queue
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* @throws NullPointerException if the specified element is null and
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* this queue does not permit null elements
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* @throws IllegalArgumentException if some property of this element
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* prevents it from being added to this queue
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*/
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public boolean add(E e) {
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if (offer(e))
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return true;
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else
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throw new IllegalStateException("Queue full");
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}
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/**
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* Retrieves and removes the head of this queue. This method differs
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* from {@link #poll poll} only in that it throws an exception if this
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* queue is empty.
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*
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* <p>This implementation returns the result of {@code poll}
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* unless the queue is empty.
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*
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* @return the head of this queue
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* @throws NoSuchElementException if this queue is empty
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*/
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public E remove() {
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E x = poll();
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if (x != null)
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return x;
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else
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throw new NoSuchElementException();
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}
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/**
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* Retrieves, but does not remove, the head of this queue. This method
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* differs from {@link #peek peek} only in that it throws an exception if
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* this queue is empty.
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*
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* <p>This implementation returns the result of {@code peek}
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* unless the queue is empty.
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*
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* @return the head of this queue
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* @throws NoSuchElementException if this queue is empty
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*/
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public E element() {
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E x = peek();
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if (x != null)
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return x;
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else
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throw new NoSuchElementException();
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}
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/**
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* Removes all of the elements from this queue.
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* The queue will be empty after this call returns.
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*
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* <p>This implementation repeatedly invokes {@link #poll poll} until it
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* returns {@code null}.
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*/
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public void clear() {
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while (poll() != null)
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;
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}
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/**
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* Adds all of the elements in the specified collection to this
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* queue. Attempts to addAll of a queue to itself result in
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* {@code IllegalArgumentException}. Further, the behavior of
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* this operation is undefined if the specified collection is
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* modified while the operation is in progress.
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*
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* <p>This implementation iterates over the specified collection,
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* and adds each element returned by the iterator to this
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* queue, in turn. A runtime exception encountered while
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* trying to add an element (including, in particular, a
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* {@code null} element) may result in only some of the elements
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* having been successfully added when the associated exception is
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* thrown.
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*
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* @param c collection containing elements to be added to this queue
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* @return {@code true} if this queue changed as a result of the call
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* @throws ClassCastException if the class of an element of the specified
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* collection prevents it from being added to this queue
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* @throws NullPointerException if the specified collection contains a
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* null element and this queue does not permit null elements,
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* or if the specified collection is null
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* @throws IllegalArgumentException if some property of an element of the
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* specified collection prevents it from being added to this
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* queue, or if the specified collection is this queue
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* @throws IllegalStateException if not all the elements can be added at
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* this time due to insertion restrictions
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* @see #add(Object)
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*/
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public boolean addAll(Collection<? extends E> c) {
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if (c == null)
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throw new NullPointerException();
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if (c == this)
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throw new IllegalArgumentException();
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boolean modified = false;
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for (E e : c)
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if (add(e))
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modified = true;
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return modified;
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}
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}
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