确定线程何时结束

1。检查线程是否完成的方法：

isalive()

• 如果线程仍在运行则返回true；否则，返回 false。
• 用于持续检查线程的状态。

加入()

• 使调用该方法的线程等待，直到指定线程完成。
• 有多种变体允许您定义最长等待时间。

2。使用 isalive() 的示例：

// verifica se as threads estão vivas
class mythread implements runnable {
    thread thrd;

    mythread(string name) {
        thrd = new thread(this, name);
        thrd.start(); // inicia a thread
    }

    public void run() {
        system.out.println(thrd.getname() + " starting.");
        try {
            for (int count = 0; count < 10; count++) {
                thread.sleep(400); // suspende a execução por 400ms
                system.out.println("in " + thrd.getname() + ", count is " + count);
            }
        } catch (interruptedexception exc) {
            system.out.println(thrd.getname() + " interrupted.");
        }
        system.out.println(thrd.getname() + " terminating.");
    }
}

class morethreads {
    public static void main(string[] args) {
        system.out.println("main thread starting.");
        mythread mt1 = new mythread("child #1");
        mythread mt2 = new mythread("child #2");
        mythread mt3 = new mythread("child #3");

        // verifica se as threads ainda estão vivas
        do {
            system.out.print(".");
            try {
                thread.sleep(100);
            } catch (interruptedexception exc) {
                system.out.println("main thread interrupted.");
            }
        } while (mt1.thrd.isalive() || mt2.thrd.isalive() || mt3.thrd.isalive());

        system.out.println("main thread ending.");
    }
}

重要要点：

• 主线程不断检查 isalive() 直到所有子线程都完成。
• 线程的执行是由 java 调度的，因此确切的输出可能会有所不同。

3。使用 join() 的示例：

// aguarda o término das threads com join()
class mythread implements runnable {
    thread thrd;

    mythread(string name) {
        thrd = new thread(this, name);
        thrd.start(); // inicia a thread
    }

    public void run() {
        system.out.println(thrd.getname() + " starting.");
        try {
            for (int count = 0; count < 10; count++) {
                thread.sleep(400); // suspende a execução por 400ms
                system.out.println("in " + thrd.getname() + ", count is " + count);
            }
        } catch (interruptedexception exc) {
            system.out.println(thrd.getname() + " interrupted.");
        }
        system.out.println(thrd.getname() + " terminating.");
    }
}

class jointhreads {
    public static void main(string[] args) {
        system.out.println("main thread starting.");
        mythread mt1 = new mythread("child #1");
        mythread mt2 = new mythread("child #2");
        mythread mt3 = new mythread("child #3");

        try {
            mt1.thrd.join(); // aguarda child #1 terminar
            system.out.println("child #1 joined.");
            mt2.thrd.join(); // aguarda child #2 terminar
            system.out.println("child #2 joined.");
            mt3.thrd.join(); // aguarda child #3 terminar
            system.out.println("child #3 joined.");
        } catch (interruptedexception exc) {
            system.out.println("main thread interrupted.");
        }

        system.out.println("main thread ending.");
    }
}

预期输出（可能会有所不同）：

Main thread starting.
Child #1 starting.
Child #2 starting.
Child #3 starting.
In Child #1, count is 0
In Child #2, count is 0
In Child #3, count is 0
...
Child #1 terminating.
Child #1 joined.
Child #2 terminating.
Child #2 joined.
Child #3 terminating.
Child #3 joined.
Main thread ending.

重要要点：

• join() 确保主线程仅在子线程完成后继续。
• 输出显示每个线程按预期顺序终止。

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