LinkedBlockingQueue常用方法

LinkedBlockingQueue是 java.util.concurrent 包下的类，是一个阻塞的线程安全的队列，底层采用链表实现。遵循FIFO(先进先出)。

LinkedBlockingQueue添加元素的方法有三个：add、put、offer。且都是向队列尾部添加元素。

LinkedBlockingQueue移除元素的方法有三个：poll、remove、take。且都是从队列中取出头部元素并从队列中删除。

LinkedBlockingQueue可以在构造函数的参数中指定大小，若没有指定大小，则默认大小为Integer.MAX_VALUE。LinkedBlockingQueue的大小不可为null。

add、offer、put的区别

add

/**
     * Inserts the specified element into this queue if it is possible to do
     * so immediately without violating capacity restrictions, returning
     * {@code true} upon success and throwing an
     * {@code IllegalStateException} if no space is currently available.
     * When using a capacity-restricted queue, it is generally preferable to
     * use {@link #offer(Object) offer}.
     *
     * @param e the element to add
     * @return {@code true} (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
     * @throws IllegalArgumentException if some property of the specified
     *         element prevents it from being added to this queue
     */
    boolean add(E e);

offer

/**
     * Inserts the specified element into this queue if it is possible to do
     * so immediately without violating capacity restrictions, returning
     * {@code true} upon success and {@code false} if no space is currently
     * available.  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 {@code true} if the element was added to this queue, else
     *         {@code false}
     * @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
     * @throws IllegalArgumentException if some property of the specified
     *         element prevents it from being added to this queue
     */
    boolean offer(E e);

put

/**
     * Inserts the specified element into this queue, 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 queue
     * @throws NullPointerException if the specified element is null
     * @throws IllegalArgumentException if some property of the specified
     *         element prevents it from being added to this queue
     */
    void put(E e) throws InterruptedException;

总结：

• add：方法在添加元素的时候，若超出了度列的长度会直接抛出异常。
• offer：方法添加元素，如果队列已满，直接返回false。
• put：方法添加元素，如果队列已满，会阻塞直到有空间可以放。

poll、remove、take的区别

poll

/**
     * Retrieves and removes the head of this queue, 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
     *        {@code unit}
     * @param unit a {@code TimeUnit} determining how to interpret the
     *        {@code timeout} parameter
     * @return the head of this queue, or {@code 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;

take

/**
     * Retrieves and removes the head of this queue, waiting if necessary
     * until an element becomes available.
     *
     * @return the head of this queue
     * @throws InterruptedException if interrupted while waiting
     */
    E take() throws InterruptedException;

remove

/**
     * Removes a single instance of the specified element from this queue,
     * if it is present.  More formally, removes an element {@code e} such
     * that {@code o.equals(e)}, if this queue contains one or more such
     * elements.
     * Returns {@code true} if this queue contained the specified element
     * (or equivalently, if this queue changed as a result of the call).
     *
     * @param o element to be removed from this queue, if present
     * @return {@code true} if this queue changed as a result of the call
     * @throws ClassCastException if the class of the specified element
     *         is incompatible with this queue
     *         (optional)
     * @throws NullPointerException if the specified element is null
     *         (optional)
     */
    boolean remove(Object o);

总结：

• poll： 若队列为空，返回null。
• take：若队列为空，发生阻塞，等待到有元素。
• remove:：若队列为空，抛出NoSuchElementException异常。