Question

我是多线程的新手，在练习时我编写了以下代码。我想调用createThred方法创建一个我称之为的新线程evrytime。但是，使用下面给出的代码，每次调用createThread方法时，我都会反复运行相同的线程。是否可以使用同一对象创建新线程？显然不是，只是想确认是否有一种我不知道的方式。

public class ThreadStartRunnable implements Runnable {

    private Thread t;
    /*
     ThreadStartRunnable(String name) {
         t = new Thread(this, name);
        t.start();
        }
     */
       private Thread createThread(String name){

         t = new Thread(this,name);
         t.start();
         return t;
     }

    /**
     * @Override run
     * 
     */
    public void run() {

        for(int i=0;i<=5;i++)
        {
            try {
                Thread.sleep(500);
            } catch (InterruptedException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
            System.out.println("The current Thread is " + t.getName() + " and thread ID is " + t.getId());
        }
    }
    /**
     * @param args
     * @throws InterruptedException 
     */
    public static void main(String[] args)  {
        // TODO Auto-generated method stub

        Thread t = Thread.currentThread();
        //new ThreadStartRunnable("User 1");
        //new ThreadStartRunnable("User 2");
        //ThreadStartRunnable c = new ThreadStartRunnable();
        ThreadStartRunnable t1 = new ThreadStartRunnable();

        t1.createThread("Child 1");
        t1.createThread("Child 2");

        for(int i=0;i<=5;i++)
        {
            try {
                Thread.sleep(1000);
            } catch (InterruptedException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
            System.out.println("The cirrent Thread is " + t.getName()+ " and thread ID is " + t.getId());
        }




    }

}

输出：

当前线程是子级2，线程ID是9

当前线程是子级2，线程ID是9

循环线程为主线程，线程ID为1

当前线程是子级2，线程ID是9

当前线程是子级2，线程ID是9

当前线程是子级2，线程ID是9

当前线程是子级2，线程ID是9

当前线程是子级2，线程ID是9

当前线程是子级2，线程ID是9

循环线程为主线程，线程ID为1

当前线程是子级2，线程ID是9

当前线程是子级2，线程ID是9

当前线程是子级2，线程ID是9

当前线程是子级2，线程ID是9

循环线程为主线程，线程ID为1

循环线程为主线程，线程ID为1

循环线程为主线程，线程ID为1

循环线程为主线程，线程ID为1

Answer 1

它始终显示Child 2的原因是因为您正在打印Thread t成员的名称，这是最后创建的线程。

替换：

System.out.println("The current Thread is " + t.getName() + " and thread ID is " + t.getId());

与

System.out.println("The current Thread is " + Thread.currentThread().getName() + " and thread ID is " + Thread.currentThread().getId());

否则可以使用相同的runnable： Initializing two threads with the same instance of a runnable

Answer 2

将run code中的代码更改为显示当前线程的名称：

System.out.println("The current Thread is " + Thread.currentThread().getName() + " and thread ID is " + Thread.currentThread().getId());

每次创建新Thread时都会覆盖实例变量t，因此使用它来跟踪线程名称和ID是不安全的。

Answer 3

您可能希望使用ExecutorService在单个对象中运行多个线程。

请看下面的代码：

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

public class Test1 {
    private ExecutorService threads;

    public Test1(int poolSize) {
        // Use fixed-size thread pool
        threads = Executors.newFixedThreadPool(poolSize);
    }

    public void createThread(String name) {
        threads.execute(new MyThread(name)); // Create MyThread
    }

    public class MyThread extends Thread {
        // Constructor passing thread name
        public MyThread(String name) {
            super(name);
        }

        @Override
        public void run() {
            for (int i = 0; i <= 5; i++) {
                try {
                    Thread.sleep(500);
                } catch (InterruptedException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
                System.out.println("The current Thread is " + super.getName()
                        + " and thread ID is " + super.getId());
            }
        }
    }

    public static void main(String[] args) {
        Thread t = Thread.currentThread();
        Test1 t1 = new Test1(3);

        t1.createThread("Child 1");
        t1.createThread("Child 2");

        for (int i = 0; i <= 5; i++) {
            try {
                Thread.sleep(1000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            System.out.println("The cirrent Thread is " + t.getName()
                    + " and thread ID is " + t.getId());
        }
    }
}

Answer 4

问题是你使用单个引用this.t来存储线程，然后当你创建第二个线程时，你覆盖那个单引用，以便它现在指向第二个线程。因此，当你打印t.getName（）时，它将引用第二个线程。

如果您希望代码按预期运行，请打印当前线程，而不是t，如下所示：

System.out.println("The current Thread is " + Thread.currentThread().getName() + " and thread ID is " + Thread.currentThread().getId());

一个对象可以在Java中创建多个线程

4 个答案: