--- jsr166/src/main/java/util/Queue.java 2003/10/19 13:38:29 1.21 +++ jsr166/src/main/java/util/Queue.java 2017/08/23 20:17:53 1.49 @@ -1,15 +1,49 @@ /* * 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/publicdomain/zero/1.0/ */ package java.util; /** * A collection designed for holding elements prior to processing. - * Besides basic {@link java.util.Collection Collection} operations, queues provide + * Besides basic {@link 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 + * {@code null} or {@code false}, depending on the operation). The + * latter form of the insert operation is designed specifically for + * use with capacity-restricted {@code Queue} implementations; in most + * implementations, insert operations cannot fail. + * + *
+ * | Throws exception | + *Returns special value | + *
---|---|---|
Insert | + *{@link #add(Object) add(e)} | + *{@link #offer(Object) 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 @@ -17,17 +51,17 @@ package java.util; * 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 + * 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 + * the tail of the queue. Other kinds of queues may use + * different placement rules. Every {@code 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 + * otherwise returning {@code 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, + * {@code offer} method is designed for use when failure is a normal, * rather than exceptional occurrence, for example, in fixed-capacity * (or "bounded") queues. * @@ -35,102 +69,115 @@ package java.util; * 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. + * implementation to implementation. The {@code remove()} and + * {@code poll()} methods differ only in their behavior when the + * queue is empty: the {@code remove()} method throws an exception, + * while the {@code poll()} method returns {@code 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 + *
The {@code Queue} interface does not define the blocking queue * methods, which are common in concurrent programming. These methods, * which wait for elements to appear or for space to become available, are * defined in the {@link java.util.concurrent.BlockingQueue} interface, which * extends this interface. * - *
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 + *
{@code Queue} implementations generally do not allow insertion + * of {@code null} elements, although some implementations, such as + * {@link LinkedList}, do not prohibit insertion of {@code null}. + * Even in the implementations that permit it, {@code null} should + * not be inserted into a {@code Queue}, as {@code null} is also + * used as a special return value by the {@code 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 + *
{@code Queue} implementations generally do not define + * element-based versions of methods {@code equals} and + * {@code hashCode} but instead inherit the identity based versions + * from class {@code 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 java.util.Collection
- * @see LinkedList
- * @see PriorityQueue
- * @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