FutureTask is base concrete implementation of Future interface and provides asynchronous processing. It contains the methods to start and cancel a task and also methods that can return the state of the FutureTask as whether it’s completed or cancelled.
We need a callable object to create a future task and then we can use Java Thread Pool Executor to process these asynchronously.
A FutureTask can be used to wrap a Callable or Runnable object. Because FutureTask implements Runnable, a FutureTask can be submitted to an Executor for execution.
Let’s see the example of FutureTask with a simple program.
Since FutureTask requires a callable object, we will create a simple Callable implementation.
Step 1st:- Create MyCallabl.java
package r4r;
import java.util.concurrent.Callable;
public class MyCallable implements Callable<String>{
private long waitTime;
public MyCallable(int timeInMillis){
this.waitTime=timeInMillis;
}
@Override
public String call() throws Exception {
Thread.sleep(waitTime);
//return the thread name executing this callable task
return Thread.currentThread().getName();
}
}
Step 2st:- Create FutureTaskExample.java
package r4r;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.FutureTask;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.TimeoutException;
public class FutureTaskExample {
public static void main(String[] args) {
MyCallable callable1 = new MyCallable(1000);
MyCallable callable2 = new MyCallable(2000);
FutureTask<String> futureTask1 = new FutureTask<String>(callable1);
FutureTask<String> futureTask2 = new FutureTask<String>(callable2);
ExecutorService executor = Executors.newFixedThreadPool(2);
executor.execute(futureTask1);
executor.execute(futureTask2);
while (true) {
try {
if(futureTask1.isDone() && futureTask2.isDone()){
System.out.println("Done");
//shut down executor service
executor.shutdown();
return;
}
if(!futureTask1.isDone()){
//wait indefinitely for future task to complete
System.out.println("FutureTask1 output="+futureTask1.get());
}
System.out.println("Waiting for FutureTask2 to complete");
String s = futureTask2.get(200L, TimeUnit.MILLISECONDS);
if(s !=null){
System.out.println("FutureTask2 output="+s);
}
} catch (InterruptedException | ExecutionException e) {
e.printStackTrace();
}catch(TimeoutException e){
//do nothing
}
}
}
}