--- jsr166/src/main/java/util/Queue.java 2003/05/27 18:20:06 1.3 +++ jsr166/src/main/java/util/Queue.java 2003/07/31 19:49:42 1.11 @@ -7,33 +7,37 @@ package java.util; /** - * A Collection designed for holding elements prior to processing. - * Besides basic {@link Collection} operations, queues provide + * 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. * *
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, 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()}. + * 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 + * returning false. This differs from the {@link java.util.Collection#add Collection.add(E)} + * 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. For example, - * in FIFO queues, they remove and return the oldest element in the queue. - * 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. + * 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, @@ -41,73 +45,86 @@ 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. * *
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.LinkedQueue
* @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
*/
public interface Queue