Difference between Runnable and Callable interface in java

Java Server Side Programming Programming

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.

Sr. No.	Key	Runnable	Callable
1	Package	It belongs to Java.lang	It belongs to java.util.concurrent
2	Thread Creation	We can create thread by passing runnable as a parameter.	We can’t create thread by passing callable as parameter
3	Return Type	Ruunable does not return anything	Callable can return results
4.	Method	It has run() method	It has call()method
5	Bulk Execution	It can’t be used for bulk execution of task	It can be used for bulk execution of task by invoking invokeAll().

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;
   }
}