Sleep/Wait/Notify/NofityAll/Synchronized

1、wait的用法

/**
 * Causes the current thread to wait until another thread invokes the * {@link java.lang.Object#notify()} method or the
 * {@link java.lang.Object#notifyAll()} method for this object.
 * In other words, this method behaves exactly as if it simply * performs the call {@code wait(0)}.
 * 

 * The current thread must own this object's monitor. The thread
 * releases ownership of this monitor and waits until another thread * notifies threads waiting on this object's monitor to wake up * either through a call to the {@code notify} method or the
 * {@code notifyAll} method. The thread then waits until it can
 * re-obtain ownership of the monitor and resumes execution. * 

 * As in the one argument version, interrupts and spurious wakeups are
 * possible, and this method should always be used in a loop: * 
 *     synchronized (obj) {
 *         while (<condition does not hold>)
 *             obj.wait(); *         ... // Perform action appropriate to condition *     } * 
 * This method should only be called by a thread that is the owner
 * of this object's monitor. See the {@code notify} method for a
 * description of the ways in which a thread can become the owner of * a monitor. * * @throws IllegalMonitorStateException  if the current thread is not
 *               the owner of the object's monitor. * @throws InterruptedException if any thread interrupted the
 *             current thread before or while the current thread *             was waiting for a notification.  The interrupted
 *             status of the current thread is cleared when
 *             this exception is thrown. * @see java.lang.Object#notify()
 * @see java.lang.Object#notifyAll()
 */
 public final void wait() throws InterruptedException {
    wait(0);
}

• 参考wait的注解， 当调用wait的时候必须要持有监视器锁，不然会跑出非法监视器异常

为什么wait()和notify()需要搭配synchonized关键字使用

2 sleep

/**
 * Causes the currently executing thread to sleep (temporarily cease * execution) for the specified number of milliseconds, subject to * the precision and accuracy of system timers and schedulers. The thread * does not lose ownership of any monitors. * * @param millis
 *         the length of time to sleep in milliseconds
 * * @throws IllegalArgumentException
 *          if the value of {@code millis} is negative
 * * @throws InterruptedException
 *          if any thread has interrupted the current thread. The * interrupted status of the current thread is
 *          cleared when this exception is thrown. 
 */
 public static native void sleep(long millis) throws InterruptedException;