Demo for java.util.concurrent.Future
/*
This program is a part of the companion code for Core Java 8th ed.
(http://horstmann.com/corejava)
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.util.ArrayList;
import java.util.Scanner;
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.Future;
import java.util.concurrent.FutureTask;
/**
* @version 1.0 2004-08-01
* @author Cay Horstmann
*/
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;
}
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