Java Thread That Will Look for New File Even After Program Has Ended

In this post, I will be showing you how to write a thread program that will keep running even after the main program has ended, and will show files at a particular location that will keep updating after you add any new files into the folder.

Prerequisite:

• Eclipse IDE
• Java 1.8

Steps:

• Right click on your project in Package Explorer, click New > Class.

Leave the package name for now and let it be default. Type any class name in the Name field, check the public static void main(String[] args) checkbox and click Finish.

• Right-click on your project again, click New > Folder.

Name the folder as "Files". Paste here your files in this folder. For now lets paste 1 file.

• Suppose let's name the class:

Class: BackgroundRunningThread.java

Code:

import java.io.File;

public class BackgroundRunningThread {

  public static void main(String[] args) {

    Runnable r = new Runnable() {

      @Override

      public void run() {

        boolean flag = true;

        while (flag) {

          File dir = new File("Files");

          File[] files = dir.listFiles();

          for (File file: files) {

            String fileName = file.getName();

            System.out.println(fileName);

          }

          try {

            Thread.sleep(2000);

          } catch (InterruptedException e) {

            e.printStackTrace();

          }

        }

      }

    };

    Thread t = new Thread(r);

    t.start();

    System.out.println("Main() program exited already\n");

  }

}

Now even if you add new files into your Files folder, this thread will keep running for infinite time ( as while(true)) and new file's name will get printed on the console.