Question

Why we need to pass the runnable instance while creating the threads using the Runnable interface?

Answer 1

The reason we need to pass the runnable object to the thread object’s constructor is that the thread must have some way to get to the run() method we want the thread to execute.

Take an e.g

public class CustomApplet extends Applet {
          public void init() {
                Runnable ot = new OurClass();
                Thread th = new Thread(ot);
                th.start();
         }
   }

Since we are no longer
overriding the run() method of the Thread class, the default run() method of the Thread class is
executed; this default run() method looks like this

public void run() {
         if (ot!= null) {
                    ot.run();
                   }
              } 

Hence, ot is the runnable object we passed to the thread’s constructor. So the thread begins execution with the run() method of the Thread class, which immediately calls the run() method of our runnable object.