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FuturesA.java Simple example of using Futures.
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Future;
import java.util.concurrent.LinkedBlockingQueue;
import java.util.concurrent.ThreadPoolExecutor;
import java.util.concurrent.TimeUnit;
public class FuturesA {
public static void run() throws Exception {
ExecutorService executor = new ThreadPoolExecutor(4, 4, 1, TimeUnit.MINUTES, new LinkedBlockingQueue<Runnable>());
Future<String> f1 = executor.submit(new CallToRemoteServiceA());
Future<String> f2 = executor.submit(new CallToRemoteServiceB());
System.out.println(f1.get() + " - " + f2.get());
}
public static void main(String args[]) {
try {
run();
} catch (Exception e) {
e.printStackTrace();
}
}
private static final class CallToRemoteServiceA implements Callable<String> {
@Override
public String call() throws Exception {
// simulate fetching data from remote service
Thread.sleep(100);
return "responseA";
}
}
private static final class CallToRemoteServiceB implements Callable<String> {
@Override
public String call() throws Exception {
// simulate fetching data from remote service
Thread.sleep(40);
return "responseB";
}
}
}

Will you consider add those after the io?

    executor.shutdown();
    executor.awaitTermination(100, TimeUnit.MILLISECONDS);
@ghost

ghost commented Oct 19, 2014

The expected output is that System.out.println(f1.get() + " - " + f2.get());
will take 140 ms to return?

No, both future will start in parallel. It will take less than (100+40) ms.

mabh commented Sep 28, 2015

expression in sysout will take approximately 100ms to get evaluated

It will take 140ms approximately if there is single core, otherwise it will do 100ms

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