Difference Between Runnable and Callable Interface in Java

Runnable and Callable both functional interface. Classes which are implementing these interfaces are designed to be executed by another thread.

Thread can be started with Ruunable and they are two ways to start a new thread: one is by subclassing Thread class and another is implementing Runnable interface.

Thread class does not have constructor for callable so we should use ExecutorService  class for executing thread.

Example of Runnable

public class RunnableExample implements Runnable {
   public void run() {
      System.out.println("Hello from a Runnable!");
   }
   public static void main(String args[]) {
      (new Thread(new RunnableExample())).start();
   }
}

Example of Callable

public class Main {
   public static void main(String args[]) throws InterruptedException, ExecutionException {
      ExecutorService services = Executors.newSingleThreadExecutor();
      Future<?> future = services.submit(new Task());
      System.out.println("In Future Object" + future.get());
   }
}
import java.util.concurrent.Callable;

public class Task implements Callable {

   @Override
   public String call() throws Exception {
      System.out.println("In call");
      String name = "test";
      return name;
   }
}