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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/licenses/publicdomain 5: */ 6: 7: package java.util; 8: 9: /** 10: * This class provides skeletal implementations of some {@link Queue} 11: * operations. The implementations in this class are appropriate when 12: * the base implementation does <em>not</em> allow <tt>null</tt> 13: * elements. Methods {@link #add add}, {@link #remove remove}, and 14: * {@link #element element} are based on {@link #offer offer}, {@link 15: * #poll poll}, and {@link #peek peek}, respectively but throw 16: * exceptions instead of indicating failure via <tt>false</tt> or 17: * <tt>null</tt> returns. 18: * 19: * <p> A <tt>Queue</tt> implementation that extends this class must 20: * minimally define a method {@link Queue#offer} which does not permit 21: * insertion of <tt>null</tt> elements, along with methods {@link 22: * Queue#peek}, {@link Queue#poll}, {@link Collection#size}, and a 23: * {@link Collection#iterator} supporting {@link 24: * Iterator#remove}. Typically, additional methods will be overridden 25: * as well. If these requirements cannot be met, consider instead 26: * subclassing {@link AbstractCollection}. 27: * 28: * <p>This class is a member of the 29: * <a href="{@docRoot}/../technotes/guides/collections/index.html"> 30: * Java Collections Framework</a>. 31: * 32: * @since 1.5 33: * @author Doug Lea 34: * @param <E> the type of elements held in this collection 35: */ 36: public abstract class AbstractQueue<E> 37: extends AbstractCollection<E> 38: implements Queue<E> { 39: 40: /** 41: * Constructor for use by subclasses. 42: */ 43: protected AbstractQueue() { 44: } 45: 46: /** 47: * Inserts the specified element into this queue if it is possible to do so 48: * immediately without violating capacity restrictions, returning 49: * <tt>true</tt> upon success and throwing an <tt>IllegalStateException</tt> 50: * if no space is currently available. 51: * 52: * <p>This implementation returns <tt>true</tt> if <tt>offer</tt> succeeds, 53: * else throws an <tt>IllegalStateException</tt>. 54: * 55: * @param e the element to add 56: * @return <tt>true</tt> (as specified by {@link Collection#add}) 57: * @throws IllegalStateException if the element cannot be added at this 58: * time due to capacity restrictions 59: * @throws ClassCastException if the class of the specified element 60: * prevents it from being added to this queue 61: * @throws NullPointerException if the specified element is null and 62: * this queue does not permit null elements 63: * @throws IllegalArgumentException if some property of this element 64: * prevents it from being added to this queue 65: */ 66: public boolean add(E e) { 67: if (offer(e)) 68: return true; 69: else 70: throw new IllegalStateException("Queue full"); 71: } 72: 73: /** 74: * Retrieves and removes the head of this queue. This method differs 75: * from {@link #poll poll} only in that it throws an exception if this 76: * queue is empty. 77: * 78: * <p>This implementation returns the result of <tt>poll</tt> 79: * unless the queue is empty. 80: * 81: * @return the head of this queue 82: * @throws NoSuchElementException if this queue is empty 83: */ 84: public E remove() { 85: E x = poll(); 86: if (x != null) 87: return x; 88: else 89: throw new NoSuchElementException(); 90: } 91: 92: /** 93: * Retrieves, but does not remove, the head of this queue. This method 94: * differs from {@link #peek peek} only in that it throws an exception if 95: * this queue is empty. 96: * 97: * <p>This implementation returns the result of <tt>peek</tt> 98: * unless the queue is empty. 99: * 100: * @return the head of this queue 101: * @throws NoSuchElementException if this queue is empty 102: */ 103: public E element() { 104: E x = peek(); 105: if (x != null) 106: return x; 107: else 108: throw new NoSuchElementException(); 109: } 110: 111: /** 112: * Removes all of the elements from this queue. 113: * The queue will be empty after this call returns. 114: * 115: * <p>This implementation repeatedly invokes {@link #poll poll} until it 116: * returns <tt>null</tt>. 117: */ 118: public void clear() { 119: while (poll() != null) 120: ; 121: } 122: 123: /** 124: * Adds all of the elements in the specified collection to this 125: * queue. Attempts to addAll of a queue to itself result in 126: * <tt>IllegalArgumentException</tt>. Further, the behavior of 127: * this operation is undefined if the specified collection is 128: * modified while the operation is in progress. 129: * 130: * <p>This implementation iterates over the specified collection, 131: * and adds each element returned by the iterator to this 132: * queue, in turn. A runtime exception encountered while 133: * trying to add an element (including, in particular, a 134: * <tt>null</tt> element) may result in only some of the elements 135: * having been successfully added when the associated exception is 136: * thrown. 137: * 138: * @param c collection containing elements to be added to this queue 139: * @return <tt>true</tt> if this queue changed as a result of the call 140: * @throws ClassCastException if the class of an element of the specified 141: * collection prevents it from being added to this queue 142: * @throws NullPointerException if the specified collection contains a 143: * null element and this queue does not permit null elements, 144: * or if the specified collection is null 145: * @throws IllegalArgumentException if some property of an element of the 146: * specified collection prevents it from being added to this 147: * queue, or if the specified collection is this queue 148: * @throws IllegalStateException if not all the elements can be added at 149: * this time due to insertion restrictions 150: * @see #add(Object) 151: */ 152: public boolean addAll(Collection<? extends E> c) { 153: if (c == null) 154: throw new NullPointerException(); 155: if (c == this) 156: throw new IllegalArgumentException(); 157: boolean modified = false; 158: Iterator<? extends E> e = c.iterator(); 159: while (e.hasNext()) { 160: if (add(e.next())) 161: modified = true; 162: } 163: return modified; 164: } 165: 166: }
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