--- jsr166/src/main/java/util/Queue.java 2003/06/07 18:31:00 1.4 +++ jsr166/src/main/java/util/Queue.java 2006/05/28 23:36:29 1.35 @@ -1,43 +1,78 @@ /* * 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. + * Expert Group and released to the public domain, as explained at + * http://creativecommons.org/licenses/publicdomain */ 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. + * A collection designed for holding elements prior to processing. + * Besides basic {@link java.util.Collection Collection} operations, + * queues provide additional insertion, extraction, and inspection + * operations. Each of these methods exists in two forms: one throws + * an exception if the operation fails, the other returns a special + * value (either null or false, depending on the + * operation). The latter form of the insert operation is designed + * specifically for use with capacity-restricted Queue + * implementations; in most implementations, insert operations cannot + * fail. + * + *
+ *
+ * | Throws exception | + *Returns special value | + *
Insert | + *{@link #add add(e)} | + *{@link #offer offer(e)} | + *
Remove | + *{@link #remove remove()} | + *{@link #poll poll()} | + *
Examine | + *{@link #element element()} | + *{@link #peek peek()} | + *
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. - * - *
The {@link #offer(E)} method adds an element if possible, otherwise - * returning false. This differs from the {@link - * Collections#add(Object)} method, which throws an unchecked exception upon - * 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. - * 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. - * 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. - * - *
The {@link #element()} and {@link #peek()} methods return but do - * not delete the element that would be obtained by a call to - * the remove and poll methods respectively. + * 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, and LIFO queues (or + * stacks) which order the elements LIFO (last-in-first-out). + * Whatever the ordering used, the head of the queue is that + * element which would be removed by a call to {@link #remove() } or + * {@link #poll()}. In a FIFO queue, all new elements are inserted at + * the tail of the queue. Other kinds of queues may use + * different placement rules. Every Queue implementation + * must specify its ordering properties. + * + *
The {@link #offer offer} method inserts an element if possible, + * otherwise returning false. This differs from the {@link + * java.util.Collection#add Collection.add} method, which can fail to + * add an element only by throwing an unchecked exception. The + * offer method is designed for use when failure 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 the head of the queue. + * Exactly which element is removed from the queue is a + * function of the queue's ordering policy, which differs from + * implementation to implementation. 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. + * + *
The {@link #element()} and {@link #peek()} methods return, but do + * not remove, the head of the queue. * *
The Queue interface does not define the blocking queue * methods, which are common in concurrent programming. These methods, @@ -45,69 +80,110 @@ package java.util; * defined in the {@link java.util.concurrent.BlockingQueue} interface, which * 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 - * by the poll method to indicate that the queue contains no - * elements. + *
Queue implementations generally do not allow insertion + * of 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. + * + *
Queue implementations generally do not define + * element-based versions of methods equals and + * hashCode but instead inherit the identity based versions + * from class Object, because element-based equality is not + * always well-defined for queues with the same elements but different + * ordering properties. + * * *
This interface is a member of the
- *
+ *
* Java Collections Framework.
*
- * @see Collection
+ * @see java.util.Collection
* @see LinkedList
* @see PriorityQueue
- * @see LinkedQueue
+ * @see java.util.concurrent.LinkedBlockingQueue
* @see java.util.concurrent.BlockingQueue
* @see java.util.concurrent.ArrayBlockingQueue
* @see java.util.concurrent.LinkedBlockingQueue
* @see java.util.concurrent.PriorityBlockingQueue
+ * @since 1.5
+ * @author Doug Lea
+ * @param