futureexample.java

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/**
 *  Example code for JavaOne hands-on J2SE lab
 *
 *  Concurrency utilities (JSR-166) example
 **/
package future;

import java.net.*;
import java.io.*;
import java.util.concurrent.*;

/**
 *  Demonstration of the use of a Future to return the results from a 
 *  Callable.  This shows the simplicity of synchronising two concurrent
 *  threads
 **/
public class FutureExample {
  /**
   *  Constructor
   **/
  public FutureExample() {
  }

  /**
   *  Run the test
   **/
  public void runTest() {
    /*  Use the Executors utility method to get an ExecutorService for a
     *  separate thread of execution
     */
    ExecutorService threadExecutor = Executors.newSingleThreadExecutor();
    System.out.println("Starting test in first thread");

    /*  Now attempt to run a task in the second thread  */
    try {
      Future<String> future = threadExecutor.submit(new CallableExample());
      /*  Set this sleep to either 100 0r 1000 to see the synchronisation
       *  effects
       */
      Thread.sleep(1000);
      System.out.println("First thread work complete.  Asking future for result");
      String result = future.get();
      System.out.println("Result from Future is " + result);
    } catch (Exception e) {
      System.out.println("Got an exception executing the test");
      System.out.println(e.getMessage());
    }

    /*  Shutdown the second thread so the program terminates gracefully
     */
    threadExecutor.shutdown();
  }

  /**
   *  Main entry point
   *
   * @param args The command line arguments
   **/
  public static void main(String[] args) {
    FutureExample fe = new FutureExample();
    fe.runTest();
  }
}