Thread() join()

public class JoinMessages extends Thread {


    public static void main(String[] args) {
        JoinMessages joinMessages = new JoinMessages();
        joinMessages.start();
    }

    public void run(){
        System.out.println(Thread.currentThread().getName()+ ":start");
        try {
            System.out.println("join start");
            join(4000);
            System.out.println("join stop");
        } catch (InterruptedException e) {
            e.printStackTrace();
        }

    }
}

来看下join（）

public final synchronized void join(long millis)
    throws InterruptedException {
        long base = System.currentTimeMillis();
        long now = 0;

        if (millis < 0) {
            throw new IllegalArgumentException("timeout value is negative");
        }

        if (millis == 0) {
            while (isAlive()) {
                wait(0);
            }
        } else {
            while (isAlive()) {
                long delay = millis - now;
                if (delay <= 0) {
                    break;
                }
                wait(delay);
                now = System.currentTimeMillis() - base;
            }
        }
    }

其实调用了wait()

public final native void wait(long timeout) throws InterruptedException;