如何从 java 中的另一个线程中断一个线程？

Question

I'm writing a simple program. A thread will run infinitely printing, say counting:

class MyThread extends Thread {
private int count = 0;
public void run() {
    while(true) {
        System.out.println(count++);

        try { currentThread().sleep(2000); }
        catch (InterruptedException ignored) { }
    }
  }
}

until user gives any (String) input of more than 2 letters:

class MyThreadStopper extends Thread {
       MyThread obj ;
       MyThreadStopper(MyThread obj) {
           this.obj = obj;
       }
     public void run() {
        String userInput ;
        while(true) {
            userInput = (new Scanner(System.in)).next();

            if( userInput.length() > 2) {
                obj.interrupt();
                currentThread().interrupt();
            }
            try{ currentThread().sleep(1000); }
            catch (InterruptedException ignored) { } 
        }
     }
  }

Used one thread for printing and another thread of different class to get input. I'm not sure where i am doing it wrong.

class temp {
    public static void main(String[] args) {
        MyThread obj = new MyThread();
        MyThreadStopper objStop = new MyThreadStopper(obj);
        obj.start();
        objStop.start();
    }
}

As it keeps printing infinitely, even though i tried printing the userInput and removing if after the userInput .

Answer 1

you are ignoring the interrupt: you could stop the thread when it is interrupted (or do something else, depeding on the requirements)

class MyThread extends Thread {
private int count = 0;
public void run() {
    while(!interrupted) {
        System.out.println(count++);

        try { currentThread().sleep(2000); }
        catch (InterruptedException e) {
            // we got interrupted, time to do something
            interrupted = true;
        }
    }
  }
}

generally interrupting a thread to stop it is rarely a good solution.

Answer 2

class MyThread extends Thread {
private int count = 0;
public void run() {
    while(true) {
        System.out.println(count++);

        try { currentThread().sleep(2000); }
        catch (InterruptedException ignored) { 
            System.out.println("Interrupted");
            break;
        }
    }
  }
}

You were not doing anything once you are catching InterruptedException. So loop was continuing. The above modified code should print "Interrupted" & break.