--- jsr166/src/main/java/util/Queue.java 2003/07/28 04:11:54 1.8 +++ jsr166/src/main/java/util/Queue.java 2003/10/18 12:29:27 1.20 @@ -8,7 +8,7 @@ package java.util; /** * A collection designed for holding elements prior to processing. - * Besides basic {@link Collection} operations, queues provide + * 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 @@ -16,17 +16,21 @@ package java.util; * 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 - * 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. - * + * 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 @@ -37,7 +41,7 @@ package java.util; * while the poll() method returns null. * *

The {@link #element()} and {@link #peek()} methods return, but do - * not delete, the head of the queue. + * 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, @@ -53,78 +57,80 @@ package java.util; * 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 java.util.concurrent.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 the base class of all elements held in this collection */ public interface Queue extends Collection { /** - * Add the specified element to this queue, if possible. + * Inserts the specified element into this queue, if possible. When + * using queues that may impose insertion restrictions (for + * example capacity bounds), method offer is generally + * preferable to method {@link Collection#add}, which can fail to + * insert an element only by throwing an exception. * - * @param element the element to add. - * @return true if it was possible to add the element to - * this queue. + * @param o the element to insert. + * @return true if it was possible to add the element to + * this queue, else false */ - boolean offer(E element); + boolean offer(E o); /** - * Retrieve and remove the head of this queue, if it is available. + * Retrieves and removes the head of this queue, or null + * if this queue is empty. * * @return the head of this queue, or null if this - * queue is empty. + * queue is empty. */ E poll(); /** - * Retrieve and remove the head of this queue. - * This method differs - * from the poll method in that it throws an exception if the - * queue is empty. + * Retrieves and removes the head of this queue. This method + * differs from the poll method in that it throws an + * exception if this queue is empty. * * @return the head of this queue. * @throws NoSuchElementException if this queue is empty. */ - E remove() throws NoSuchElementException; + E remove(); /** - * Retrieve, but do not remove, the head of this queue, or null - * if this queue is empty. This method differs from the poll - * method only in that this method does not remove the element from - * this queue. + * Retrieves, but does not remove, the head of this queue, + * returning null if this queue is empty. * - * @return the head of this queue, or null if this queue is empty. + * @return the head of this queue, or null if this queue + * is empty. */ E peek(); /** - * Retrieve, but do not remove, the head of this queue. This method - * differs from the peek method only in that it throws an + * Retrieves, but does not remove, the head of this queue. This method + * differs from the peek method only in that it throws an * exception if this queue is empty. * * @return the head of this queue. * @throws NoSuchElementException if this queue is empty. */ - E element() throws NoSuchElementException; + E element(); } - - - - - - - - - -