Java java.util.concurrent.Future的一个例子

package callableTest;
import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;
class CallableIndicator{
  private String name;
  private Double result;
  static public final int TIME = 3000;
  public CallableIndicator(String name, Double result){
    this.name = name;
    this.result = result;
  }
  public Double getResult(){
    return this.result;
  }
  public String getName(){
    return this.name;
  }
}
public class CallableTest {
   private static final int POOL_SIZE = 2;
      static class CalcThread implements Callable<CallableIndicator> {
        private String name;
          private List<Double> dataList = new ArrayList<>();
          public CalcThread(String name) {
              for(int i = 0; i < 10000; ++i) {
                  dataList.add(Math.random());
              }
              this.name = name;
              System.out.println("In CalcThread constructor, thread id: " + 
              Thread.currentThread().getId());
          }
          @Override
          public CallableIndicator call() throws Exception {
              double total = 0;
              for(Double d : dataList) {
                  total += d;
              }
              System.out.println("In CalcThread @Override call(), thread id: " + 
                    Thread.currentThread().getId());
              Thread.sleep(CallableIndicator.TIME);
              return new CallableIndicator(this.name, total / dataList.size());
          }
      }
      public static void printThread(){
        System.out.println("In main Thread? " + Thread.currentThread().getId());
      }
      public static void main(String[] args) {
        long start = System.currentTimeMillis();
          List<Future<CallableIndicator>> fList = new ArrayList<>();
          ExecutorService es = Executors.newFixedThreadPool(POOL_SIZE);
          printThread();
          System.out.println("Ready to submit new thread...");
          for(int i = 0; i < POOL_SIZE; ++i) {
              fList.add(es.submit(new CalcThread("Jerry Thread: " + i)));
          }
          for(Future<CallableIndicator> f : fList) {
              try {
                /*
                 * 注意这个get是异步操作：The result can only be retrieved using method get when the computation has completed, blocking if necessary until it is ready. 
                 */
                  System.out.println("Thread name: " + f.get().getName() + " result: " +  f.get().getResult());
              } catch (Exception e) {
                  e.printStackTrace();
              }
          }
          long end = System.currentTimeMillis();
          System.out.println("duration: " + ( end - start));
          es.shutdown();
      }
}