1 /* 2 * Written by Doug Lea with assistance from members of JCP JSR-166 3 * Expert Group and released to the public domain, as explained at 4 * http://creativecommons.org/publicdomain/zero/1.0/ 5 */ 6 7 package java.util; 8 9 // BEGIN android-note 10 // removed link to collections framework docs 11 // END android-note 12 13 /** 14 * This class provides skeletal implementations of some {@link Queue} 15 * operations. The implementations in this class are appropriate when 16 * the base implementation does <em>not</em> allow <tt>null</tt> 17 * elements. Methods {@link #add add}, {@link #remove remove}, and 18 * {@link #element element} are based on {@link #offer offer}, {@link 19 * #poll poll}, and {@link #peek peek}, respectively, but throw 20 * exceptions instead of indicating failure via <tt>false</tt> or 21 * <tt>null</tt> returns. 22 * 23 * <p>A <tt>Queue</tt> implementation that extends this class must 24 * minimally define a method {@link Queue#offer} which does not permit 25 * insertion of <tt>null</tt> elements, along with methods {@link 26 * Queue#peek}, {@link Queue#poll}, {@link Collection#size}, and 27 * {@link Collection#iterator}. Typically, additional methods will be 28 * overridden as well. If these requirements cannot be met, consider 29 * instead subclassing {@link AbstractCollection}. 30 * 31 * @since 1.5 32 * @author Doug Lea 33 * @param <E> the type of elements held in this collection 34 */ 35 public abstract class AbstractQueue<E> 36 extends AbstractCollection<E> 37 implements Queue<E> { 38 39 /** 40 * Constructor for use by subclasses. 41 */ AbstractQueue()42 protected AbstractQueue() { 43 } 44 45 /** 46 * Inserts the specified element into this queue if it is possible to do so 47 * immediately without violating capacity restrictions, returning 48 * <tt>true</tt> upon success and throwing an <tt>IllegalStateException</tt> 49 * if no space is currently available. 50 * 51 * <p>This implementation returns <tt>true</tt> if <tt>offer</tt> succeeds, 52 * else throws an <tt>IllegalStateException</tt>. 53 * 54 * @param e the element to add 55 * @return <tt>true</tt> (as specified by {@link Collection#add}) 56 * @throws IllegalStateException if the element cannot be added at this 57 * time due to capacity restrictions 58 * @throws ClassCastException if the class of the specified element 59 * prevents it from being added to this queue 60 * @throws NullPointerException if the specified element is null and 61 * this queue does not permit null elements 62 * @throws IllegalArgumentException if some property of this element 63 * prevents it from being added to this queue 64 */ add(E e)65 public boolean add(E e) { 66 if (offer(e)) 67 return true; 68 else 69 throw new IllegalStateException("Queue full"); 70 } 71 72 /** 73 * Retrieves and removes the head of this queue. This method differs 74 * from {@link #poll poll} only in that it throws an exception if this 75 * queue is empty. 76 * 77 * <p>This implementation returns the result of <tt>poll</tt> 78 * unless the queue is empty. 79 * 80 * @return the head of this queue 81 * @throws NoSuchElementException if this queue is empty 82 */ remove()83 public E remove() { 84 E x = poll(); 85 if (x != null) 86 return x; 87 else 88 throw new NoSuchElementException(); 89 } 90 91 /** 92 * Retrieves, but does not remove, the head of this queue. This method 93 * differs from {@link #peek peek} only in that it throws an exception if 94 * this queue is empty. 95 * 96 * <p>This implementation returns the result of <tt>peek</tt> 97 * unless the queue is empty. 98 * 99 * @return the head of this queue 100 * @throws NoSuchElementException if this queue is empty 101 */ element()102 public E element() { 103 E x = peek(); 104 if (x != null) 105 return x; 106 else 107 throw new NoSuchElementException(); 108 } 109 110 /** 111 * Removes all of the elements from this queue. 112 * The queue will be empty after this call returns. 113 * 114 * <p>This implementation repeatedly invokes {@link #poll poll} until it 115 * returns <tt>null</tt>. 116 */ clear()117 public void clear() { 118 while (poll() != null) 119 ; 120 } 121 122 /** 123 * Adds all of the elements in the specified collection to this 124 * queue. Attempts to addAll of a queue to itself result in 125 * <tt>IllegalArgumentException</tt>. Further, the behavior of 126 * this operation is undefined if the specified collection is 127 * modified while the operation is in progress. 128 * 129 * <p>This implementation iterates over the specified collection, 130 * and adds each element returned by the iterator to this 131 * queue, in turn. A runtime exception encountered while 132 * trying to add an element (including, in particular, a 133 * <tt>null</tt> element) may result in only some of the elements 134 * having been successfully added when the associated exception is 135 * thrown. 136 * 137 * @param c collection containing elements to be added to this queue 138 * @return <tt>true</tt> if this queue changed as a result of the call 139 * @throws ClassCastException if the class of an element of the specified 140 * collection prevents it from being added to this queue 141 * @throws NullPointerException if the specified collection contains a 142 * null element and this queue does not permit null elements, 143 * or if the specified collection is null 144 * @throws IllegalArgumentException if some property of an element of the 145 * specified collection prevents it from being added to this 146 * queue, or if the specified collection is this queue 147 * @throws IllegalStateException if not all the elements can be added at 148 * this time due to insertion restrictions 149 * @see #add(Object) 150 */ addAll(Collection<? extends E> c)151 public boolean addAll(Collection<? extends E> c) { 152 if (c == null) 153 throw new NullPointerException("c == null"); 154 if (c == this) 155 throw new IllegalArgumentException("c == this"); 156 boolean modified = false; 157 for (E e : c) 158 if (add(e)) 159 modified = true; 160 return modified; 161 } 162 163 } 164