一：sleep 和 wait

sleep()方法：

功能：讓當前線程休眠指定時間，休眠時間的準確性依賴于系統時鐘和CPU調度機制

是Thread類的靜態方法

可在任何地方調用，需要處理InterruptedException

當前線程調用sleep()方法，當前線程會進入阻塞狀態，sleep()結束進入可執行狀態

sleep()方法不釋放已獲取的鎖資源

wait()方法：

讓當前線程進入等待狀態，當別的其他線程調用notify()或者notifyAll()方法時，當前線程進入可運行狀態

是Object類的成員方法

wait方法必須在同步上下文中調用，例如：同步方法塊或者同步方法中，這也就意味著如果你想要調用wait方法，前提是必須獲取對象上的鎖資源

當wait方法調用時，當前線程將會釋放已獲取的對象鎖資源，并進入等待隊列，其他線程就可以嘗試獲取對象上的鎖資源

sleep() vs wait()

sleepwait

同步	不需要在同步方法或同步塊中調用	只能在同步上下文中調用wait方法，否則或拋出IllegalMonitorStateException異常
作用對象	定義在java.lang.Thread中，作用于當前線程	定義在Object類中，作用于對象本身
釋放鎖資源	否	是
喚醒條件	超時或者調用interrupt()方法	其他線程調用對象的notify()或者notifyAll()方法
方法屬性	sleep是靜態方法	wait是實例方法

二：方法簽名：

sleep()方法是Thread類的靜態方法

/*** 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類的成員方法

/*** 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);}

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