--- jsr166/src/main/java/util/Queue.java 2003/05/18 18:10:02 1.2 +++ jsr166/src/main/java/util/Queue.java 2003/06/23 02:26:15 1.6 @@ -1,15 +1,21 @@ +/* + * Written by Doug Lea with assistance from members of JCP JSR-166 + * Expert Group and released to the public domain. Use, modify, and + * redistribute this code in any way without acknowledgement. + */ + package java.util; /** * A Collection designed for holding elements prior to processing. * Besides basic {@link Collection} operations, queues provide * additional insertion, extraction, and inspection operations. - * +0 * *

Queues typically, but do not necessarily, order elements in a - * FIFO (first-in-first-out) manner. Among the exceptions are priority - * queues, which order elements according to a supplied comparators, or - * the elements natural ordering. Every Queue implementation must specify - * its ordering guarantees. + * FIFO (first-in-first-out) manner. Among the exceptions are + * priority queues, which order elements according to a supplied + * comparator, or the elements' natural ordering. Every Queue + * implementation must specify its ordering guarantees. * *

The {@link #offer(E)} method adds an element if possible, otherwise * returning false. This differs from the {@link @@ -17,10 +23,14 @@ package java.util; * failure. It is designed for use in collections in which failure to * add is a normal, rather than exceptional occurrence, for example, * in fixed-capacity (or “bounded”) queues. - * + + * *

The {@link #remove()} and {@link #poll()} methods remove and return an - * element in accord with the implementation's ordering policy. For example, - * in FIFO queues, they remove and return the oldest element in the queue. + * element in accord with the implementation's ordering policy. + * Exactly which element is removed from the queue is a function + * of the queue's ordering policy, which differs from implementation + * to implementation. Possible orderings include (but are not limited + * to) first-in-first-out (FIFO), last-in-first-out (LIFO), element priority, and arbitrary. * The remove() and poll() methods differ only in their * behavior when the queue is empty: the remove() method throws an * exception, while the poll() method returns null. @@ -36,8 +46,10 @@ package java.util; * extends this interface. * *

Queue implementations generally do not allow insertion of - * null elements. Even in the few implementations that permit it, - * it is a bad idea, as null is also used as a special return value + * null elements, although some implementations, such as + * {@link LinkedList}, do not prohibit insertion of null. + * Even in the implementations that permit it, null should not be inserted into + * a Queue, as null is also used as a special return value * by the poll method to indicate that the queue contains no * elements. * @@ -48,7 +60,7 @@ package java.util; * @see Collection * @see LinkedList * @see PriorityQueue - * @see LinkedQueue + * @see java.util.concurrent.LinkedQueue * @see java.util.concurrent.BlockingQueue * @see java.util.concurrent.ArrayBlockingQueue * @see java.util.concurrent.LinkedBlockingQueue @@ -65,20 +77,16 @@ public interface Queue extends Collec /** * Remove and return an element from the queue if one is available. - * Exactly which element is removed from the queue is a function - * of the queue's ordering policy, which differs from implementation - * to implementation. Possible orderings include (but are not limited - * to) first-in-first-out (FIFO), element priority, and arbitrary. * * @return an element previously on the queue, or null if the - * queue is empty. + * queue is empty. */ public E poll(); /** * Remove and return an element from the queue. This method differs * from the poll method in that it throws an exception if the - * queue is empty. + * queue is empty. * * @return an element previously on the queue. * @throws NoSuchElementException if the queue is empty.