Question

问题 - 创建N个线程（例如3，名称可以是Thread-1，Thread-2，Thread-3），它们会以相反的顺序说出HelloWorld，即First Thread-3会说HelloWorld，然后是Thread-2然后是Thread -1

解决方案 - 上述问题可以通过各种方式解决，例如使用volatile标志来指示必须运行哪个线程或使用join方法（以便Thread-1完成依赖于Thread-2和Thread-2＆s;线程3）。我试图通过join方法解决这个问题。但它没有给我正确的结果。请帮我。以下是我的计划 -

Thread [] previosThread = {null};
    int[] previousIndex = {0};
    for (int i=3; i>=1; i--) {
        int currentIndex = i;
        System.out.print("PreviousIndex--"+previousIndex[0]+"  ;  ");
        System.out.println("CurrentIndex--"+currentIndex);
        Thread newThread = new Thread("Thread-"+i) {
            public void run() {
                if(previousIndex[0]!=0 && previousIndex[0]==currentIndex+1) {
                    try {
                        previosThread[0].join();
                    } catch (InterruptedException e) {
                        Thread.currentThread().interrupt();
                    }
                }
                System.out.println(this.getName()+" is saying HelloWorld!!");
            }
        };
        previosThread[0] = newThread;
        previousIndex[0] = currentIndex;
        newThread.start();
    }

以上程序给出了不确定的输出，如下所示 -

PreviousIndex - 0; CURRENTINDEX - 3 PreviousIndex - 3; CURRENTINDEX - 2 PreviousIndex - 2; CURRENTINDEX - 1 Thread-2说HelloWorld !! Thread-1正在说HelloWorld !! Thread-3正在说HelloWorld !!

Answer 1

Andreas＆＃39;评论，我错误地使用了previosThread [0]。我没有使用previosThread [0]，而是维护了一个单独的创建线程数组，这样我就可以在新线程上正确调用join方法，然后以相反的顺序启动这个数组的每个线程，以便正确地处理join方法，这两个调用方都是和依赖的线程应该运行。以下是我的代码---

public class AntThread extends Thread {

private Thread dependentThread;
private String threadName;
private int index;
public AntThread(Thread dependentThread, String threadName, int index) {
    super(threadName);
    this.dependentThread = dependentThread;
    this.threadName = threadName;
    this.index = index;
}

public void run() {
    if(dependentThread!=null) {
        try {
            dependentThread.join();
        } catch (InterruptedException e) {
            this.interrupt();
        }
    }
    System.out.println(Thread.currentThread().getName()+" is saying - HelloWorld");
}

}

和主要类 -

public class MultipleThreadsGreetingInReverseOrderTest {

public static void main(String[] args) throws InterruptedException {

    int size = 10;
    Thread [] createdThreads = new Thread[size];
    for(int i=size; i>0; i--) {
        Thread dependentThread = null;
        if(i!=size)
            dependentThread = createdThreads[i];
        Thread antThread = new AntThread(dependentThread, "Thread-"+i, i);
        createdThreads[i-1] = antThread;
    }

    //Starting the last thread first, as the join condition will work only when dependent thread is runnning
    for(int j=createdThreads.length-1; j>=0; j--) {
        createdThreads[j].start();
    }

}

}

非常感谢Andreas !!为了快速回应。

join（）方法在我实现的代码中无法正常工作

1 个答案: