Java 多線程：join__Java

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join() 方法是 java.lang.Thread 類的執行個體方法，方法簽名

public final void join() throws InterruptedException

public final void join(long millis) throws InterruptedException

public final void join(long millis, int nanos) throws InterruptedException

join() 方法使得一個線程在另一個線程結束後再執行，如果在一個線程執行個體上調用，當前啟動並執行線程將阻塞直至調用 join() 方法的線程執行個體結束

join() 方法接收 long 型別參數，使得在等待特定毫秒後線程失效

Waits at most millis milliseconds for this thread to die. A timeout of 0 means to wait forever. 

join() 方法還可以額外接收一個 int 型別參數

Waits at most millis milliseconds plus nanos nanoseconds for this thread to die. 

樣本：

public static void main(String[] args) throws InterruptedException {    Thread t1 = new Thread(new Runnable() {        @Override        public void run() {            System.out.println("First thread started!");            System.out.println("Ready to sleep 5 seconds!");            try {                Thread.sleep(5000);            } catch (InterruptedException e) {                e.printStackTrace();            }            System.out.println("First thread ended!");        }    });    Thread t2 = new Thread(new Runnable() {        @Override        public void run() {            System.out.println("Second thread started!");            System.out.println("Second thread ended!");        }    });    t1.start();    t1.join();    t2.start();}

如果注釋掉 t1.join();，運行結果：

去掉注釋後運行結果：

給 join() 方法傳入一個 long 型別參數，使得最長等待 3 秒

public static void main(String[] args) throws InterruptedException {    Thread t1 = new Thread(new Runnable() {        @Override        public void run() {            System.out.println("First thread started!");            System.out.println("Ready to sleep 5 seconds!");            try {                Thread.sleep(5000);            } catch (InterruptedException e) {                e.printStackTrace();            }            System.out.println("First thread ended!");        }    });    Thread t2 = new Thread(new Runnable() {        @Override        public void run() {            System.out.println("Second thread started!");            System.out.println("Second thread ended!");        }    });    t1.start();    t1.join(3000);    t2.start();}

運行結果：