In Java there are two ways to implement a class whose instances are to be executed by a thread.
- By implementing Runnable interface.
- By implementing Callable interface.
But what if you have a Runnable and you want to convert it into a Callable in Java at runtime. Executors class in Java provides utility methods to do that conversion.
- callable(Runnable task)– Returns a Callable object that, when called, runs the given task and returns null.
- callable(Runnable task, T result)– Returns a Callable object that, when called, runs the given task and returns the given result.
Converting Runnable to Callable in Java
1- Using the first method – callable(Runnable task)
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public class RunnableToCallable { public static void main(String[] args) { ExecutorService es = Executors.newFixedThreadPool(2); // converting runnable task to callable Callable<Object> callable = Executors.callable(new MyRunnable()); // submit method Future<Object> f = es.submit(callable); try { System.out.println("Result- " + f.get()); } catch (InterruptedException | ExecutionException e) { // TODO Auto-generated catch block e.printStackTrace(); } es.shutdown(); } } class MyRunnable implements Runnable{ @Override public void run() { System.out.println("Running task.."); } } |
Output
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Running task.. Result- null |
2- Using the second method- callable(Runnable task, T result)
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public class RunnableToCallable { public static void main(String[] args) { ExecutorService es = Executors.newFixedThreadPool(2); // converting runnable task to callable Callable<String> callable = Executors.callable(new MyRunnable(), "From callable"); // submit method Future<String> f = es.submit(callable); try { System.out.println("Result- " + f.get()); } catch (InterruptedException | ExecutionException e) { // TODO Auto-generated catch block e.printStackTrace(); } es.shutdown(); } } class MyRunnable implements Runnable{ @Override public void run() { System.out.println("Running task.."); } } |
Output
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Running task.. Result- From callable |
That’s all for the topic How to Convert a Runnable into a Callable in Java. If something is missing or you have something to share about the topic please write a comment.
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