Question

If an Exception occurs at some point in Java code, the control goes to the catch block. However, If this code is actually inside a multi-threaded run() method, how do I instruct the code the to finish with the run() method when the Exception occurs?

In other words, how can I instruct the thread that the run() method has finished, because it knows that an Exception has occurred?

Answer 1

If you’re in the run() method of your Thread, you can simply return, which terminates the Thread in the same way that calling return in any other method ends the method processing.

Maybe something like this, where you watch for an Exception and call return if the Exception occurs…

public void run() {
    try {
        // your code goes here
    }
    catch (Exception e) {
        return;
    }
}

However, if your Thread has multiple methods, the best way might be to have each method declare that it can throw an Exception. For example, if your Thread is like this…

public MyThread extends Thread {

    public void run() {
        try {
            runLongTask1();
            runLongTask2();
        }
        catch (Exception e) {
            return;
        }
    }

    public void runLongTask1() throws Exception {
        // your code here
    }

    public void runLongTask2() throws Exception {
        // your code here
    }
}

See how each of the other methods can throw an Exception. So, if an Exception is thrown in any of the methods of this Thread, it will trigger the try-catch of the run() method, and return out of the Thread, thus terminating it.

Of course, if the try-catch in your run() method covers all the code of the method, you don’t need to actually return, because it is implicit when it reaches the end of the run() method anyway.