| Runnable | Callable |
|---|---|
| It belongs to Java.lang Package | It belongs to java.util.concurrent Package |
| Runnable is introduced in JDK 1.0 | Callable is introduced in JDK 5.0 |
| Runnable interface has run()
method. The return type of the run() method is void. |
Callable interface has call()
method. The return type of the call() method is an Future object. |
| run() method can't throw checked exception. | call() method can throw checked exception |
| Runnable use execute() method to put the task in queue. | Callable use submit() method to put the task in queue. |
| We can create thread by passing runnable as a parameter. |
We
can’t create thread by passing callable
as parameter. Because there is no constructor defined in the Thread class which accepts a Callable interface. So to execute a Callable instance, you have to use the ExecutorService interface of the Java 5 Executor framework. Using submit() method. |
Single Abstract Method : Both have a single abstract method run()
method in Runnable and call() method in Callable interface. That means both
are functional interfaces and can be used in Lambda expressions since Java8.
new Thread( () -> System.out.println("Runnable") ).start()
Both can be used with the Executors framework. Executors framework defines
ExecutorService interface which can accept and execute Runnable and Callable
using submit() method.
We can convert Runnable to Callable by using utility method provided by
Executors class.
Callable callable = Executors.callable(Runnable task);
Note that Future.get() is a
blocking method. Its blocks until execution is finished, so we should use
this method with a timeout to avoid deadlock or livelock in our application.
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