Thread 實例的 join() 方法可用于將一個線程的執行開始“連接”到另一個線程的執行結束，以便一個線程在另一個線程結束之前不會開始運行。如果在 Thread 實例上調用 join()，則當前正在運行的線程將阻塞，直到 Thread 實例完成執行但是如果 ia 有多個線程并且當我在循環內調用 join 時。所有線程并行運行。但是根據連接概念，首先連接的線程應該完成，然后只有主線程應該允許連接其他線程。public class MultiThreading implements Runnable {private int name;public MultiThreading(int number) {    name =number;}@Overridepublic void run() {    for (int i = 0; i <= 10; i++ ) {           System.out.println("Thread number :" + name +" Printed value "+i);        try {            Thread.sleep(100);        } catch (final InterruptedException e) {            return;        }    }}public static void main(String[] args) throws InterruptedException {    final Thread[] workers = new Thread[3];    for (int i = 0; i < nthreads; ++i) {        workers[i] = new Thread(new MultiThreading(i));    }    for (final Thread t : workers) {        t.start();    }    for (final Thread t : workers) {        t.join();        System.out.println("Thread joind to main thread : " + t.getName());    }    System.out.println("Main thread ends");}}在上面的代碼中，如果第一個線程被加入，那么主線程應該被阻塞并且不應該讓其他線程加入（直到被加入的線程完成run方法的執行）。但是所有線程都是并行連接的。輸出就像 -Thread number :0 Printed value 0Thread number :1 Printed value 0Thread number :2 Printed value 0Thread number :0 Printed value 1Thread number :1 Printed value 1Thread number :2 Printed value 1Thread number :0 Printed value 2Thread number :1 Printed value 2Thread number :2 Printed value 2Thread number :0 Printed value 3Thread number :1 Printed value 3Thread number :2 Printed value 3Thread number :0 Printed value 4Thread number :1 Printed value 4Thread number :2 Printed value 4Thread number :1 Printed value 5