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Callable and Future in Java
java.util.concurrent.The callable object can return the computed result done by a thread in contrast to a runnable interface which can only run the thread. The Callable object returns a Future object which provides methods to monitor the progress of a task being executed by a thread. The future object can be used to check the status of a Callable and then retrieve the result from the Callable once the thread is done. It also provides timeout functionality.
Syntax
//submit the callable using ThreadExecutor //and get the result as a Future object Future<Long> result10 = executor.submit(new FactorialService(10)); //get the result using get method of the Future object //get method waits till the thread execution and then return the result of the execution. Long factorial10 = result10.get();
Example
The following TestThread program shows usage of Futures and Callables in the thread based environment.
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;
public class TestThread {
public static void main(final String[] arguments) throws InterruptedException, ExecutionException {
ExecutorService executor = Executors.newSingleThreadExecutor();
System.out.println("Factorial Service called for 10!");
Future<Long> result10 = executor.submit(new FactorialService(10));
System.out.println("Factorial Service called for 20!");
Future<Long> result20 = executor.submit(new FactorialService(20));
Long factorial10 = result10.get();
System.out.println("10! = " + factorial10);
Long factorial20 = result20.get();
System.out.println("20! = " + factorial20);
executor.shutdown();
}
static class FactorialService implements Callable<Long> {
private int number;
public FactorialService(int number) {
this.number = number;
}
@Override
public Long call() throws Exception {
return factorial();
}
private Long factorial() throws InterruptedException {
long result = 1;
while (number != 0) {
result = number * result;
number--;
Thread.sleep(100);
}
return result;
}
}
}This will produce the following result.
Output
Factorial Service called for 10! Factorial Service called for 20! 10! = 3628800 20! = 2432902008176640000
Updated on: 18-Jun-2020
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