一：sleep 和 wait

sleep()方法：

1. 功能：让当前线程休眠指定时间，休眠时间的准确性依赖于系统时钟和CPU调度机制
2. 是Thread类的静态方法
3. 可在任何地方调用，需要处理InterruptedException
4. 当前线程调用sleep()方法，当前线程会进入阻塞状态，sleep()结束进入可执行状态
5. sleep()方法不释放已获取的锁资源

wait()方法：

1. 让当前线程进入等待状态，当别的其他线程调用notify()或者notifyAll()方法时，当前线程进入可运行状态
2. 是Object类的成员方法
3. wait方法必须在同步上下文中调用，例如：同步方法块或者同步方法中，这也就意味着如果你想要调用wait方法，前提是必须获取对象上的锁资源
4. 当wait方法调用时，当前线程将会释放已获取的对象锁资源，并进入等待队列，其他线程就可以尝试获取对象上的锁资源

sleep() vs wait()

	sleep	wait
同步	不需要在同步方法或同步块中调用	只能在同步上下文中调用wait方法，否则或抛出IllegalMonitorStateException异常
作用对象	定义在java.lang.Thread中，作用于当前线程	定义在Object类中，作用于对象本身
释放锁资源	否	是
唤醒条件	超时或者调用interrupt()方法	其他线程调用对象的notify()或者notifyAll()方法
方法属性	sleep是静态方法	wait是实例方法

二：方法签名：

sleep()方法是Thread类的静态方法

/*** 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*          <i>interrupted status</i> of the current thread is*          cleared when this exception is thrown.*/public static native void sleep(long millis) throws InterruptedException;

wait()方法是Object类的成员方法

/*** 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)}.* <p>* 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.* <p>* As in the one argument version, interrupts and spurious wakeups are* possible, and this method should always be used in a loop:* <pre>*     synchronized (obj) {*         while (&lt;condition does not hold&gt;)*             obj.wait();*         ... // Perform action appropriate to condition*     }* </pre>* 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 <i>interrupted*             status</i> 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);}