public interface Callable<V>
{V call() throws Exception;
}

public interface Future<V>
{ V get() throws ...;V get(long timeout, Timeout unit) throws ...;void cancel(boolean mayInterrupt);boolean isCancelled();boolean isDone();
}

Callable<Integer> myComputation = ...;
FutureTask<Integer> task = new FutureTask<Integer>(myComputation);
Thread t = new Thread(task);//it's a Runnable
t.start();
...
Integer result = task.get();//it's a Future

class MatchCounter implements Callable<Integer>
{public MatchCounter(File directory,String keyword){...}public Integer call() {...}//return the number of matching files
}

FutureTask<Integer> task = new FutureTask<Integer>(counter);
Thread t = new Thread(task);
t.start();

System.out.println(task.get()+" matching files.");

for(Future<Integer> result: results)count += result.get();

import java.io.*;
import java.util.*;
import java.util.concurrent.*;public class FutureTest
{public static void main(String[] args){Scanner in = new Scanner(System.in);System.out.print("Enter base directory (e.g. /usr/local/jdk5.0/src): ");String directory = in.nextLine();System.out.print("Enter keyword (e.g. volatile): ");String keyword = in.nextLine();MatchCounter counter = new MatchCounter(new File(directory), keyword);FutureTask<Integer> task = new FutureTask<Integer>(counter);Thread t = new Thread(task);t.start();try{System.out.println(task.get() + " matching files.");}catch (ExecutionException e){e.printStackTrace();}catch (InterruptedException e){}}
}/*** This task counts the files in a directory and its subdirectories that contain a given keyword.*/
class MatchCounter implements Callable<Integer>
{/*** Constructs a MatchCounter.* @param directory the directory in which to start the search* @param keyword the keyword to look for*/public MatchCounter(File directory, String keyword){this.directory = directory;this.keyword = keyword;}public Integer call(){count = 0;try{File[] files = directory.listFiles();ArrayList<Future<Integer>> results = new ArrayList<Future<Integer>>();for (File file : files)if (file.isDirectory()){MatchCounter counter = new MatchCounter(file, keyword);FutureTask<Integer> task = new FutureTask<Integer>(counter);results.add(task);Thread t = new Thread(task);t.start();}else{if (search(file)) count++;}for (Future<Integer> result : results)try{count += result.get();}catch (ExecutionException e){e.printStackTrace();}}catch (InterruptedException e){}return count;}/*** Searches a file for a given keyword.* @param file the file to search* @return true if the keyword is contained in the file*/public boolean search(File file){try{Scanner in = new Scanner(new FileInputStream(file));boolean found = false;while (!found && in.hasNextLine()){String line = in.nextLine();if (line.contains(keyword)) found = true;}in.close();return found;}catch (IOException e){return false;}}private File directory;private String keyword;private int count;
}