Difference between Callable and Runnable in Java

Programming

by Adminstrator | 10-Aug-2020

Tags: Callable Runnable FunctionalInterface Concurrency Multithreading

Both topics are related to concurrency in Java. Both of these Functional Interfaces are used to create a separate thread of execution. Let�s take a closer look:

Runnable(I)

Runnable was introduced into Java 1.0. The limitation of runnable is that we cannot return anything back from it or throw an exception.
Steps to create a thread using runnable interface:
1. Override the run method()

@Override
Public void run(){
	//statements;
}

2. Pass the runnable into Thread class

Thread thread = new Thread(new Runnable());

3. Start the thread by calling start() method on thread class object.

thread.start();

Program

public class ThreadUsingRunnable implements Runnable {
    @Override
    public void run() {
        System.out.println("Inside the run() method.");
    }
    public static void main(String[] args) {
        ThreadUsingRunnable runnable = new ThreadUsingRunnable();
        Thread thread = new Thread(runnable);
        thread.start();
    }
}

Output

Inside the run() method.

Callable(I)

Callable was introduced in Java 1.5.
Steps to create a thread using callable interface:
1. Override the run() method

@Override
Public  call() throws Exception{
	//statements;
}

2. Convert the callable to runnable because thread class doesn�t has a constructor which takes callable as a parameter.

FutureTask futureTask = new FutureTask<>(new MyCallable());

3. Pass the converted runnable to Thread class

Thread thread = new Thread(futureTask);

4. Start the thread by calling start() method on thread class object

thread.start();

Program

 public class ThreadUsingCallable implements Callable {
    @Override
    public String call() throws Exception {
        return "Inside the call() method.";
    }
    public static void main(String[] args) throws InterruptedException, ExecutionException {
        ThreadUsingCallable callable = new ThreadUsingCallable();
        FutureTask futureTask = new FutureTask<>(callable);
        Thread thread = new Thread(futureTask);
        thread.start();
        System.out.println(futureTask.get());
    }
}

Output

Inside the call() method.

Differences in tabular form

Runnable(I)	Callable(I)
Introduced in Java 1.0	Introduced in Java 1.5
run() method needs to be overridden. public abstract void run();	call() method needs to be overridden V call() throws Exception;
Run() method cannot return any value back to the calling thread.	Call() method can return any type of value back to the calling thread
run() method cannot throw a check exception	call() method can throw any checked exception
Thread class constructor can take a runnable object as a parameter	There is no constructor in thread class which takes a callable object, therefore callable must be converted to runnable type

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