/* * 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/publicdomain/zero/1.0/ */ package java.util.concurrent; import java.util.*; /** * A {@link Deque} that additionally supports blocking operations that wait * for the deque to become non-empty when retrieving an element, and wait for * space to become available in the deque when storing an element. * *

BlockingDeque methods come in four forms, with different ways * of handling operations that cannot be satisfied immediately, but may be * satisfied at some point in the future: * one throws an exception, the second returns a special value (either * null or false, depending on the operation), the third * blocks the current thread indefinitely until the operation can succeed, * and the fourth blocks for only a given maximum time limit before giving * up. These methods are summarized in the following table: * *

* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
First Element (Head)
Throws exceptionSpecial valueBlocksTimes out
Insert{@link #addFirst addFirst(e)}{@link #offerFirst(Object) offerFirst(e)}{@link #putFirst putFirst(e)}{@link #offerFirst(Object, long, TimeUnit) offerFirst(e, time, unit)}
Remove{@link #removeFirst removeFirst()}{@link #pollFirst pollFirst()}{@link #takeFirst takeFirst()}{@link #pollFirst(long, TimeUnit) pollFirst(time, unit)}
Examine{@link #getFirst getFirst()}{@link #peekFirst peekFirst()}not applicablenot applicable
Last Element (Tail)
Throws exceptionSpecial valueBlocksTimes out
Insert{@link #addLast addLast(e)}{@link #offerLast(Object) offerLast(e)}{@link #putLast putLast(e)}{@link #offerLast(Object, long, TimeUnit) offerLast(e, time, unit)}
Remove{@link #removeLast() removeLast()}{@link #pollLast() pollLast()}{@link #takeLast takeLast()}{@link #pollLast(long, TimeUnit) pollLast(time, unit)}
Examine{@link #getLast getLast()}{@link #peekLast peekLast()}not applicablenot applicable
* *

Like any {@link BlockingQueue}, a BlockingDeque is thread safe, * does not permit null elements, and may (or may not) be * capacity-constrained. * *

A BlockingDeque implementation may be used directly as a FIFO * BlockingQueue. The methods inherited from the * BlockingQueue interface are precisely equivalent to * BlockingDeque methods as indicated in the following table: * *

* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
BlockingQueue Method Equivalent BlockingDeque Method
Insert
{@link #add(Object) add(e)}{@link #addLast(Object) addLast(e)}
{@link #offer(Object) offer(e)}{@link #offerLast(Object) offerLast(e)}
{@link #put(Object) put(e)}{@link #putLast(Object) putLast(e)}
{@link #offer(Object, long, TimeUnit) offer(e, time, unit)}{@link #offerLast(Object, long, TimeUnit) offerLast(e, time, unit)}
Remove
{@link #remove() remove()}{@link #removeFirst() removeFirst()}
{@link #poll() poll()}{@link #pollFirst() pollFirst()}
{@link #take() take()}{@link #takeFirst() takeFirst()}
{@link #poll(long, TimeUnit) poll(time, unit)}{@link #pollFirst(long, TimeUnit) pollFirst(time, unit)}
Examine
{@link #element() element()}{@link #getFirst() getFirst()}
{@link #peek() peek()}{@link #peekFirst() peekFirst()}
* *

Memory consistency effects: As with other concurrent * collections, actions in a thread prior to placing an object into a * {@code BlockingDeque} * happen-before * actions subsequent to the access or removal of that element from * the {@code BlockingDeque} in another thread. * *

This interface is a member of the * * Java Collections Framework. * * @since 1.6 * @author Doug Lea * @param the type of elements held in this collection */ public interface BlockingDeque extends BlockingQueue, Deque { /* * We have "diamond" multiple interface inheritance here, and that * introduces ambiguities. Methods might end up with different * specs depending on the branch chosen by javadoc. Thus a lot of * methods specs here are copied from superinterfaces. */ /** * Inserts the specified element at the front of this deque if it is * possible to do so immediately without violating capacity restrictions, * throwing an IllegalStateException if no space is currently * available. When using a capacity-restricted deque, it is generally * preferable to use {@link #offerFirst(Object) offerFirst}. * * @param e the element to add * @throws IllegalStateException {@inheritDoc} * @throws ClassCastException {@inheritDoc} * @throws NullPointerException if the specified element is null * @throws IllegalArgumentException {@inheritDoc} */ void addFirst(E e); /** * Inserts the specified element at the end of this deque if it is * possible to do so immediately without violating capacity restrictions, * throwing an IllegalStateException if no space is currently * available. When using a capacity-restricted deque, it is generally * preferable to use {@link #offerLast(Object) offerLast}. * * @param e the element to add * @throws IllegalStateException {@inheritDoc} * @throws ClassCastException {@inheritDoc} * @throws NullPointerException if the specified element is null * @throws IllegalArgumentException {@inheritDoc} */ void addLast(E e); /** * Inserts the specified element at the front of this deque if it is * possible to do so immediately without violating capacity restrictions, * returning true upon success and false if no space is * currently available. * When using a capacity-restricted deque, this method is generally * preferable to the {@link #addFirst(Object) addFirst} method, which can * fail to insert an element only by throwing an exception. * * @param e the element to add * @throws ClassCastException {@inheritDoc} * @throws NullPointerException if the specified element is null * @throws IllegalArgumentException {@inheritDoc} */ boolean offerFirst(E e); /** * Inserts the specified element at the end of this deque if it is * possible to do so immediately without violating capacity restrictions, * returning true upon success and false if no space is * currently available. * When using a capacity-restricted deque, this method is generally * preferable to the {@link #addLast(Object) addLast} method, which can * fail to insert an element only by throwing an exception. * * @param e the element to add * @throws ClassCastException {@inheritDoc} * @throws NullPointerException if the specified element is null * @throws IllegalArgumentException {@inheritDoc} */ boolean offerLast(E e); /** * Inserts the specified element at the front of this deque, * waiting if necessary for space to become available. * * @param e the element to add * @throws InterruptedException if interrupted while waiting * @throws ClassCastException if the class of the specified element * prevents it from being added to this deque * @throws NullPointerException if the specified element is null * @throws IllegalArgumentException if some property of the specified * element prevents it from being added to this deque */ void putFirst(E e) throws InterruptedException; /** * Inserts the specified element at the end of this deque, * waiting if necessary for space to become available. * * @param e the element to add * @throws InterruptedException if interrupted while waiting * @throws ClassCastException if the class of the specified element * prevents it from being added to this deque * @throws NullPointerException if the specified element is null * @throws IllegalArgumentException if some property of the specified * element prevents it from being added to this deque */ void putLast(E e) throws InterruptedException; /** * Inserts the specified element at the front of this deque, * waiting up to the specified wait time if necessary for space to * become available. * * @param e the element to add * @param timeout how long to wait before giving up, in units of * unit * @param unit a TimeUnit determining how to interpret the * timeout parameter * @return true if successful, or false if * the specified waiting time elapses before space is available * @throws InterruptedException if interrupted while waiting * @throws ClassCastException if the class of the specified element * prevents it from being added to this deque * @throws NullPointerException if the specified element is null * @throws IllegalArgumentException if some property of the specified * element prevents it from being added to this deque */ boolean offerFirst(E e, long timeout, TimeUnit unit) throws InterruptedException; /** * Inserts the specified element at the end of this deque, * waiting up to the specified wait time if necessary for space to * become available. * * @param e the element to add * @param timeout how long to wait before giving up, in units of * unit * @param unit a TimeUnit determining how to interpret the * timeout parameter * @return true if successful, or false if * the specified waiting time elapses before space is available * @throws InterruptedException if interrupted while waiting * @throws ClassCastException if the class of the specified element * prevents it from being added to this deque * @throws NullPointerException if the specified element is null * @throws IllegalArgumentException if some property of the specified * element prevents it from being added to this deque */ boolean offerLast(E e, long timeout, TimeUnit unit) throws InterruptedException; /** * Retrieves and removes the first element of this deque, waiting * if necessary until an element becomes available. * * @return the head of this deque * @throws InterruptedException if interrupted while waiting */ E takeFirst() throws InterruptedException; /** * Retrieves and removes the last element of this deque, waiting * if necessary until an element becomes available. * * @return the tail of this deque * @throws InterruptedException if interrupted while waiting */ E takeLast() throws InterruptedException; /** * Retrieves and removes the first element of this deque, waiting * up to the specified wait time if necessary for an element to * become available. * * @param timeout how long to wait before giving up, in units of * unit * @param unit a TimeUnit determining how to interpret the * timeout parameter * @return the head of this deque, or null if the specified * waiting time elapses before an element is available * @throws InterruptedException if interrupted while waiting */ E pollFirst(long timeout, TimeUnit unit) throws InterruptedException; /** * Retrieves and removes the last element of this deque, waiting * up to the specified wait time if necessary for an element to * become available. * * @param timeout how long to wait before giving up, in units of * unit * @param unit a TimeUnit determining how to interpret the * timeout parameter * @return the tail of this deque, or null if the specified * waiting time elapses before an element is available * @throws InterruptedException if interrupted while waiting */ E pollLast(long timeout, TimeUnit unit) throws InterruptedException; /** * Removes the first occurrence of the specified element from this deque. * If the deque does not contain the element, it is unchanged. * More formally, removes the first element e such that * o.equals(e) (if such an element exists). * Returns true if this deque contained the specified element * (or equivalently, if this deque changed as a result of the call). * * @param o element to be removed from this deque, if present * @return true if an element was removed as a result of this call * @throws ClassCastException if the class of the specified element * is incompatible with this deque * (optional) * @throws NullPointerException if the specified element is null * (optional) */ boolean removeFirstOccurrence(Object o); /** * Removes the last occurrence of the specified element from this deque. * If the deque does not contain the element, it is unchanged. * More formally, removes the last element e such that * o.equals(e) (if such an element exists). * Returns true if this deque contained the specified element * (or equivalently, if this deque changed as a result of the call). * * @param o element to be removed from this deque, if present * @return true if an element was removed as a result of this call * @throws ClassCastException if the class of the specified element * is incompatible with this deque * (optional) * @throws NullPointerException if the specified element is null * (optional) */ boolean removeLastOccurrence(Object o); // *** BlockingQueue methods *** /** * Inserts the specified element into the queue represented by this deque * (in other words, at the tail of this deque) if it is possible to do so * immediately without violating capacity restrictions, returning * true upon success and throwing an * IllegalStateException if no space is currently available. * When using a capacity-restricted deque, it is generally preferable to * use {@link #offer(Object) offer}. * *

This method is equivalent to {@link #addLast(Object) addLast}. * * @param e the element to add * @throws IllegalStateException {@inheritDoc} * @throws ClassCastException if the class of the specified element * prevents it from being added to this deque * @throws NullPointerException if the specified element is null * @throws IllegalArgumentException if some property of the specified * element prevents it from being added to this deque */ boolean add(E e); /** * Inserts the specified element into the queue represented by this deque * (in other words, at the tail of this deque) if it is possible to do so * immediately without violating capacity restrictions, returning * true upon success and false if no space is currently * available. When using a capacity-restricted deque, this method is * generally preferable to the {@link #add} method, which can fail to * insert an element only by throwing an exception. * *

This method is equivalent to {@link #offerLast(Object) offerLast}. * * @param e the element to add * @throws ClassCastException if the class of the specified element * prevents it from being added to this deque * @throws NullPointerException if the specified element is null * @throws IllegalArgumentException if some property of the specified * element prevents it from being added to this deque */ boolean offer(E e); /** * Inserts the specified element into the queue represented by this deque * (in other words, at the tail of this deque), waiting if necessary for * space to become available. * *

This method is equivalent to {@link #putLast(Object) putLast}. * * @param e the element to add * @throws InterruptedException {@inheritDoc} * @throws ClassCastException if the class of the specified element * prevents it from being added to this deque * @throws NullPointerException if the specified element is null * @throws IllegalArgumentException if some property of the specified * element prevents it from being added to this deque */ void put(E e) throws InterruptedException; /** * Inserts the specified element into the queue represented by this deque * (in other words, at the tail of this deque), waiting up to the * specified wait time if necessary for space to become available. * *

This method is equivalent to * {@link #offerLast(Object,long,TimeUnit) offerLast}. * * @param e the element to add * @return true if the element was added to this deque, else * false * @throws InterruptedException {@inheritDoc} * @throws ClassCastException if the class of the specified element * prevents it from being added to this deque * @throws NullPointerException if the specified element is null * @throws IllegalArgumentException if some property of the specified * element prevents it from being added to this deque */ boolean offer(E e, long timeout, TimeUnit unit) throws InterruptedException; /** * Retrieves and removes the head of the queue represented by this deque * (in other words, the first element of this deque). * This method differs from {@link #poll poll} only in that it * throws an exception if this deque is empty. * *

This method is equivalent to {@link #removeFirst() removeFirst}. * * @return the head of the queue represented by this deque * @throws NoSuchElementException if this deque is empty */ E remove(); /** * Retrieves and removes the head of the queue represented by this deque * (in other words, the first element of this deque), or returns * null if this deque is empty. * *

This method is equivalent to {@link #pollFirst()}. * * @return the head of this deque, or null if this deque is empty */ E poll(); /** * Retrieves and removes the head of the queue represented by this deque * (in other words, the first element of this deque), waiting if * necessary until an element becomes available. * *

This method is equivalent to {@link #takeFirst() takeFirst}. * * @return the head of this deque * @throws InterruptedException if interrupted while waiting */ E take() throws InterruptedException; /** * Retrieves and removes the head of the queue represented by this deque * (in other words, the first element of this deque), waiting up to the * specified wait time if necessary for an element to become available. * *

This method is equivalent to * {@link #pollFirst(long,TimeUnit) pollFirst}. * * @return the head of this deque, or null if the * specified waiting time elapses before an element is available * @throws InterruptedException if interrupted while waiting */ E poll(long timeout, TimeUnit unit) throws InterruptedException; /** * Retrieves, but does not remove, the head of the queue represented by * this deque (in other words, the first element of this deque). * This method differs from {@link #peek peek} only in that it throws an * exception if this deque is empty. * *

This method is equivalent to {@link #getFirst() getFirst}. * * @return the head of this deque * @throws NoSuchElementException if this deque is empty */ E element(); /** * Retrieves, but does not remove, the head of the queue represented by * this deque (in other words, the first element of this deque), or * returns null if this deque is empty. * *

This method is equivalent to {@link #peekFirst() peekFirst}. * * @return the head of this deque, or null if this deque is empty */ E peek(); /** * Removes the first occurrence of the specified element from this deque. * If the deque does not contain the element, it is unchanged. * More formally, removes the first element e such that * o.equals(e) (if such an element exists). * Returns true if this deque contained the specified element * (or equivalently, if this deque changed as a result of the call). * *

This method is equivalent to * {@link #removeFirstOccurrence(Object) removeFirstOccurrence}. * * @param o element to be removed from this deque, if present * @return true if this deque changed as a result of the call * @throws ClassCastException if the class of the specified element * is incompatible with this deque * (optional) * @throws NullPointerException if the specified element is null * (optional) */ boolean remove(Object o); /** * Returns true if this deque contains the specified element. * More formally, returns true if and only if this deque contains * at least one element e such that o.equals(e). * * @param o object to be checked for containment in this deque * @return true if this deque contains the specified element * @throws ClassCastException if the class of the specified element * is incompatible with this deque * (optional) * @throws NullPointerException if the specified element is null * (optional) */ public boolean contains(Object o); /** * Returns the number of elements in this deque. * * @return the number of elements in this deque */ public int size(); /** * Returns an iterator over the elements in this deque in proper sequence. * The elements will be returned in order from first (head) to last (tail). * * @return an iterator over the elements in this deque in proper sequence */ Iterator iterator(); // *** Stack methods *** /** * Pushes an element onto the stack represented by this deque. In other * words, inserts the element at the front of this deque unless it would * violate capacity restrictions. * *

This method is equivalent to {@link #addFirst(Object) addFirst}. * * @throws IllegalStateException {@inheritDoc} * @throws ClassCastException {@inheritDoc} * @throws NullPointerException if the specified element is null * @throws IllegalArgumentException {@inheritDoc} */ void push(E e); }