1 /* 2 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 3 * 4 * This code is free software; you can redistribute it and/or modify it 5 * under the terms of the GNU General Public License version 2 only, as 6 * published by the Free Software Foundation. Oracle designates this 7 * particular file as subject to the "Classpath" exception as provided 8 * by Oracle in the LICENSE file that accompanied this code. 9 * 10 * This code is distributed in the hope that it will be useful, but WITHOUT 11 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 12 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 13 * version 2 for more details (a copy is included in the LICENSE file that 14 * accompanied this code). 15 * 16 * You should have received a copy of the GNU General Public License version 17 * 2 along with this work; if not, write to the Free Software Foundation, 18 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 19 * 20 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 21 * or visit www.oracle.com if you need additional information or have any 22 * questions. 23 */ 24 25 /* 26 * This file is available under and governed by the GNU General Public 27 * License version 2 only, as published by the Free Software Foundation. 28 * However, the following notice accompanied the original version of this 29 * file: 30 * 31 * Written by Doug Lea with assistance from members of JCP JSR-166 32 * Expert Group and released to the public domain, as explained at 33 * http://creativecommons.org/publicdomain/zero/1.0/ 34 */ 35 36 package java.util; 37 38 /** 39 * This class provides skeletal implementations of some {@link Queue} 40 * operations. The implementations in this class are appropriate when 41 * the base implementation does <em>not</em> allow <tt>null</tt> 42 * elements. Methods {@link #add add}, {@link #remove remove}, and 43 * {@link #element element} are based on {@link #offer offer}, {@link 44 * #poll poll}, and {@link #peek peek}, respectively, but throw 45 * exceptions instead of indicating failure via <tt>false</tt> or 46 * <tt>null</tt> returns. 47 * 48 * <p>A <tt>Queue</tt> implementation that extends this class must 49 * minimally define a method {@link Queue#offer} which does not permit 50 * insertion of <tt>null</tt> elements, along with methods {@link 51 * Queue#peek}, {@link Queue#poll}, {@link Collection#size}, and 52 * {@link Collection#iterator}. Typically, additional methods will be 53 * overridden as well. If these requirements cannot be met, consider 54 * instead subclassing {@link AbstractCollection}. 55 * 56 * <p>This class is a member of the 57 * <a href="{@docRoot}/../technotes/guides/collections/index.html"> 58 * Java Collections Framework</a>. 59 * 60 * @since 1.5 61 * @author Doug Lea 62 * @param <E> the type of elements held in this collection 63 */ 64 public abstract class AbstractQueue<E> 65 extends AbstractCollection<E> 66 implements Queue<E> { 67 68 /** 69 * Constructor for use by subclasses. 70 */ AbstractQueue()71 protected AbstractQueue() { 72 } 73 74 /** 75 * Inserts the specified element into this queue if it is possible to do so 76 * immediately without violating capacity restrictions, returning 77 * <tt>true</tt> upon success and throwing an <tt>IllegalStateException</tt> 78 * if no space is currently available. 79 * 80 * <p>This implementation returns <tt>true</tt> if <tt>offer</tt> succeeds, 81 * else throws an <tt>IllegalStateException</tt>. 82 * 83 * @param e the element to add 84 * @return <tt>true</tt> (as specified by {@link Collection#add}) 85 * @throws IllegalStateException if the element cannot be added at this 86 * time due to capacity restrictions 87 * @throws ClassCastException if the class of the specified element 88 * prevents it from being added to this queue 89 * @throws NullPointerException if the specified element is null and 90 * this queue does not permit null elements 91 * @throws IllegalArgumentException if some property of this element 92 * prevents it from being added to this queue 93 */ add(E e)94 public boolean add(E e) { 95 if (offer(e)) 96 return true; 97 else 98 throw new IllegalStateException("Queue full"); 99 } 100 101 /** 102 * Retrieves and removes the head of this queue. This method differs 103 * from {@link #poll poll} only in that it throws an exception if this 104 * queue is empty. 105 * 106 * <p>This implementation returns the result of <tt>poll</tt> 107 * unless the queue is empty. 108 * 109 * @return the head of this queue 110 * @throws NoSuchElementException if this queue is empty 111 */ remove()112 public E remove() { 113 E x = poll(); 114 if (x != null) 115 return x; 116 else 117 throw new NoSuchElementException(); 118 } 119 120 /** 121 * Retrieves, but does not remove, the head of this queue. This method 122 * differs from {@link #peek peek} only in that it throws an exception if 123 * this queue is empty. 124 * 125 * <p>This implementation returns the result of <tt>peek</tt> 126 * unless the queue is empty. 127 * 128 * @return the head of this queue 129 * @throws NoSuchElementException if this queue is empty 130 */ element()131 public E element() { 132 E x = peek(); 133 if (x != null) 134 return x; 135 else 136 throw new NoSuchElementException(); 137 } 138 139 /** 140 * Removes all of the elements from this queue. 141 * The queue will be empty after this call returns. 142 * 143 * <p>This implementation repeatedly invokes {@link #poll poll} until it 144 * returns <tt>null</tt>. 145 */ clear()146 public void clear() { 147 while (poll() != null) 148 ; 149 } 150 151 /** 152 * Adds all of the elements in the specified collection to this 153 * queue. Attempts to addAll of a queue to itself result in 154 * <tt>IllegalArgumentException</tt>. Further, the behavior of 155 * this operation is undefined if the specified collection is 156 * modified while the operation is in progress. 157 * 158 * <p>This implementation iterates over the specified collection, 159 * and adds each element returned by the iterator to this 160 * queue, in turn. A runtime exception encountered while 161 * trying to add an element (including, in particular, a 162 * <tt>null</tt> element) may result in only some of the elements 163 * having been successfully added when the associated exception is 164 * thrown. 165 * 166 * @param c collection containing elements to be added to this queue 167 * @return <tt>true</tt> if this queue changed as a result of the call 168 * @throws ClassCastException if the class of an element of the specified 169 * collection prevents it from being added to this queue 170 * @throws NullPointerException if the specified collection contains a 171 * null element and this queue does not permit null elements, 172 * or if the specified collection is null 173 * @throws IllegalArgumentException if some property of an element of the 174 * specified collection prevents it from being added to this 175 * queue, or if the specified collection is this queue 176 * @throws IllegalStateException if not all the elements can be added at 177 * this time due to insertion restrictions 178 * @see #add(Object) 179 */ addAll(Collection<? extends E> c)180 public boolean addAll(Collection<? extends E> c) { 181 if (c == null) 182 throw new NullPointerException(); 183 if (c == this) 184 throw new IllegalArgumentException(); 185 boolean modified = false; 186 for (E e : c) 187 if (add(e)) 188 modified = true; 189 return modified; 190 } 191 192 } 193