ExecutionCallback allows you to asynchronously get notified when the execution is done. When implementing ExecutionCallback.done(Future) method, you can check if the task is already cancelled.

import com.hazelcast.core.Hazelcast;
import com.hazelcast.core.ExecutionCallback;
import com.hazelcast.core.DistributedTask;
import java.util.concurrent.ExecutorService;    
import java.util.concurrent.Future; 
        
ExecutorService es = Hazelcast.getExecutorService();
DistributedTask<String> task = new DistributedTask<String>(new Fibonacci<Long>(10));
task.setExecutionCallback(new ExecutionCallback<Long> () {
    public void done (Future<Long> future) { 
        try {
            if (! future.isCancelled()) {
                System.out.println("Fibonacci calculation result = " + future.get());
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
});
es.execute(task);

You could have achieved the same results by extending DistributedTask and overriding the DistributedTask.done() method.

import com.hazelcast.core.Hazelcast;
import com.hazelcast.core.DistributedTask;
import java.util.concurrent.ExecutorService;    
import java.util.concurrent.Future; 
        
ExecutorService es = Hazelcast.getExecutorService();
es.execute(new DistributedTask<String>(new Fibonacci<Long>(10)) {
    public void done () { 
        try {
            if (! isCancelled()) {
                System.out.println("Fibonacci calculation result = " + get());
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
});