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Diffstat (limited to 'libjava/classpath/external/jsr166/java/util/Queue.java')
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diff --git a/libjava/classpath/external/jsr166/java/util/Queue.java b/libjava/classpath/external/jsr166/java/util/Queue.java new file mode 100644 index 000000000..5711545b0 --- /dev/null +++ b/libjava/classpath/external/jsr166/java/util/Queue.java @@ -0,0 +1,189 @@ +/* + * Written by Doug Lea with assistance from members of JCP JSR-166 + * 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 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 <tt>null</tt> or <tt>false</tt>, depending on the + * operation). The latter form of the insert operation is designed + * specifically for use with capacity-restricted <tt>Queue</tt> + * implementations; in most implementations, insert operations cannot + * fail. + * + * <p> + * <table BORDER CELLPADDING=3 CELLSPACING=1> + * <tr> + * <td></td> + * <td ALIGN=CENTER><em>Throws exception</em></td> + * <td ALIGN=CENTER><em>Returns special value</em></td> + * </tr> + * <tr> + * <td><b>Insert</b></td> + * <td>{@link #add add(e)}</td> + * <td>{@link #offer offer(e)}</td> + * </tr> + * <tr> + * <td><b>Remove</b></td> + * <td>{@link #remove remove()}</td> + * <td>{@link #poll poll()}</td> + * </tr> + * <tr> + * <td><b>Examine</b></td> + * <td>{@link #element element()}</td> + * <td>{@link #peek peek()}</td> + * </tr> + * </table> + * + * <p>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 + * 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 <em>head</em> 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 <em> tail</em> of the queue. Other kinds of queues may use + * different placement rules. Every <tt>Queue</tt> implementation + * must specify its ordering properties. + * + * <p>The {@link #offer offer} method inserts an element if possible, + * otherwise returning <tt>false</tt>. 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 + * <tt>offer</tt> method is designed for use when failure is a normal, + * rather than exceptional occurrence, for example, in fixed-capacity + * (or "bounded") queues. + * + * <p>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 <tt>remove()</tt> and + * <tt>poll()</tt> methods differ only in their behavior when the + * queue is empty: the <tt>remove()</tt> method throws an exception, + * while the <tt>poll()</tt> method returns <tt>null</tt>. + * + * <p>The {@link #element()} and {@link #peek()} methods return, but do + * not remove, the head of the queue. + * + * <p>The <tt>Queue</tt> interface does not define the <i>blocking queue + * methods</i>, 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. + * + * <p><tt>Queue</tt> implementations generally do not allow insertion + * of <tt>null</tt> elements, although some implementations, such as + * {@link LinkedList}, do not prohibit insertion of <tt>null</tt>. + * Even in the implementations that permit it, <tt>null</tt> should + * not be inserted into a <tt>Queue</tt>, as <tt>null</tt> is also + * used as a special return value by the <tt>poll</tt> method to + * indicate that the queue contains no elements. + * + * <p><tt>Queue</tt> implementations generally do not define + * element-based versions of methods <tt>equals</tt> and + * <tt>hashCode</tt> but instead inherit the identity based versions + * from class <tt>Object</tt>, because element-based equality is not + * always well-defined for queues with the same elements but different + * ordering properties. + * + * + * <p>This interface is a member of the + * <a href="{@docRoot}/../technotes/guides/collections/index.html"> + * Java Collections Framework</a>. + * + * @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 <E> the type of elements held in this collection + */ +public interface Queue<E> extends Collection<E> { + /** + * Inserts the specified element into this queue if it is possible to do so + * immediately without violating capacity restrictions, returning + * <tt>true</tt> upon success and throwing an <tt>IllegalStateException</tt> + * if no space is currently available. + * + * @param e the element to add + * @return <tt>true</tt> (as specified by {@link Collection#add}) + * @throws IllegalStateException if the element cannot be added at this + * time due to capacity restrictions + * @throws ClassCastException if the class of the specified element + * prevents it from being added to this queue + * @throws NullPointerException if the specified element is null and + * this queue does not permit null elements + * @throws IllegalArgumentException if some property of this element + * prevents it from being added to this queue + */ + boolean add(E e); + + /** + * Inserts the specified element into this queue if it is possible to do + * so immediately without violating capacity restrictions. + * When using a capacity-restricted queue, this method is generally + * preferable to {@link #add}, which can fail to insert an element only + * by throwing an exception. + * + * @param e the element to add + * @return <tt>true</tt> if the element was added to this queue, else + * <tt>false</tt> + * @throws ClassCastException if the class of the specified element + * prevents it from being added to this queue + * @throws NullPointerException if the specified element is null and + * this queue does not permit null elements + * @throws IllegalArgumentException if some property of this element + * prevents it from being added to this queue + */ + boolean offer(E e); + + /** + * Retrieves and removes the head of this queue. This method differs + * from {@link #poll poll} 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 remove(); + + /** + * Retrieves and removes the head of this queue, + * or returns <tt>null</tt> if this queue is empty. + * + * @return the head of this queue, or <tt>null</tt> if this queue is empty + */ + E poll(); + + /** + * Retrieves, but does not remove, the head of this queue. This method + * differs from {@link #peek peek} 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(); + + /** + * Retrieves, but does not remove, the head of this queue, + * or returns <tt>null</tt> if this queue is empty. + * + * @return the head of this queue, or <tt>null</tt> if this queue is empty + */ + E peek(); +} |