Threads; Creating a separate thread to periodically do something

Question

As an addition to my current application, I need to create a separate thread which will periodically do some processing

I've create a new class to do all this, and this class will be loaded on startup of my application.

This is what I have so far :

public class PeriodicChecker extends Thread
{
    static
    {
        Thread t = new Thread(new PeriodicChecker());
        while(true)
        {
            t.run();
            try
            {
                Thread.sleep(5000l);
            }
            catch (InterruptedException e)
            {
                e.printStackTrace();
            }
        }
    }

    /**
     * Private constructor to prevent instantiation
     */
    private PeriodicChecker()
    {

    }

    @Override
    public void run()
    {
        System.out.println("Thread is doing something");
        // Actual business logic here, that is repeated
    }

}

I want to make constructor private to prevent other people from attempting to instantiate this class accidentally. How can I achieve this?

Also, is there anything bad about my implementation of such requirements? I'm only creating one thread which will run then sleep, have I missed anything obvious? I haven't worked with threads before

Answer 1

Java offers ScheduledExecutorService to schedule and run periodic tasks or tasks with delay. It should provide all the features you need. Timer is another class that offers similar functionalities, but I would recommend the ScheduledExecutorService over Timer for its flexibility of configuration and better error management.

Answer 2

You have some conceptual erros in your code... for example:

• You should call start() and not run(), because you are running the method sequentially and not simultaneously.
• You can call start() only once, not once in each loop iteration. After that, the thread is in state TERMINATED, you should create a new thread to run it again
• You should not create the thread in the static block, it is a bad practice, and maybe the Thread is running before you want it to run.

You should read some examples about thread, it is a little difficult to unserstand at the beginning, and you can have undesired effects very easily.

Here is a little example, that may do something similar to that you want:

public class PeriodicChecker extends Thread
{
    @Override
    public void run()
    {
        while(true) {
           System.out.println("Thread is doing something");
           Thread.sleep(5000);
        }
    }

}

public OtherClass {
   public static void main(String args[]) {
      Thread t = new PeriodicChecker();
      t.start();
   }
}

If you want that none can create a new Thread, you could create a singleton, so you will be sure that none is creating more threads.