Stopping the threads

Starting a thread is very easy in java, after you create it you need to call the method start(), for example:

Thread myThread = new Thread(new MyRunnable());
myThread.start();

where MyRunnable is a class implementing the Runnable interface overidden the method run().

The creation of a thread using the constructor with argument a class implementing Runnable is one of two way to create a thread, the other is to extend the class Thread, and after you call the method start() to execute the thread.

Instead, stopping the thread is much more complicated, there is a method stop() but it is deprecated.

There are two ways to stop a thread:

1. setting a flag
   consider a thread created with this Runnable:

   public class RunnableA implements Runnable {
   
       private volatile boolean running;
   
       public boolean isRunning() {
   	return running;
       }
   
       public void setRunning(boolean running) {
   	this.running = running;
       }
   
       @Override
       public void run() {
   	running = true;
   	while (running) {
   	    // the thread job
   	}
   	running = false;
       }
   
   }
   

   the field “running” is used in the method run() as condition to execute the loop, setting to false the method run() returns and the thread stops.
   In order to stop a thread with this Runnable you need the line:

   myThread.setRunning(false);
   

   Note that the field “running” is volatile so that any thread accessing to “running” gets the latest value.

2. calling the method interrupt()
   with the line:

   myThread.interrupt();
   

   the thread is stopped at the first call of a method throwing the exception InterruptedException, for example wait(), join() and sleep(), as in the following:

   public class RunnableB1 implements Runnable {
   
       @Override
       public void run() {
   
   	while (true) {
   	    // the thread job
   	    try {
   		Thread.sleep(1000);
   	    } catch (InterruptedException e) {
   		e.printStackTrace();
   	    }
   	}
   
       }
   
   }
   

   If no method throwing an InterruptedException is in the code then the you have to check if the method interrupt() is called:

   public class RunnableB2 implements Runnable {
   
       @Override
       public void run() {
   
   	while (!Thread.interrupted()) {
   	    // the thread job
   	}
   
       }
   
   }