Find files with certain extension only using FilenameFilter in Java

Byron KiourtzoglouFebruary 18th, 2013Last Updated: February 18th, 2013

0 117 1 minute read

In this tutorial we are going to show you how to use the FilenameFilter interface in Java in order to list all the file with a certain property in their names. In this example for instance, we just want to print all the text files in a specific directory, hence the files ending with the “.txt” extension. Instances of classes that implement this interface are used to filter file names. These instances are used to filter directory listings in the list method of class File.

In short to delete files with certain extensions using FilenameFilter you have to:

Create a class that implements the FilenameFilter interface and override the accept method to perform the filtering you want in the filename.
Use the above class as the argument in the list method, when listing the files of the target directory.

So here is the FileFilter class the implements FilenameFilter interface:

FileFilter.java

package com.javacodegeeks.java.core;

import java.io.File;
import java.io.FilenameFilter;

public class FileFilter implements FilenameFilter {

	private String fileExtension;

	public FileFilter(String fileExtension) {
		this.fileExtension = fileExtension;
	}

	@Override
	public boolean accept(File directory, String fileName) {
		return (fileName.endsWith(this.fileExtension));
	}
}

DeleteTextFiles.java

package com.javacodegeeks.java.core;

import java.io.File;

public class FindTextFiles {

	private static String parentDirectory = "C:\\Users\\nikos7\\Desktop\\files";
	private static String fileExtension = ".txt";

	public static void main(String[] args) {
		FileFilter fileFilter = new FileFilter(fileExtension);
		File parentDir = new File(parentDirectory);

		// Put the names of all files ending with .txt in a String array
		String[] listOfTextFiles = parentDir.list(fileFilter);

		if (listOfTextFiles.length == 0) {
			System.out.println("There are no text files in this direcotry!");
			return;
		}

		System.out.println("I found these files with "+fileExtension+" extension:");

		for (String file : listOfTextFiles) {

			//construct the absolute file paths...
			String absoluteFilePath = new StringBuffer(parentDirectory).append(File.separator).append(file).toString();

			System.out.println(absoluteFilePath);
		}
	}
}

Output:

I found these files with .txt extension:
C:\Users\nikos7\Desktop\files\file1.txt
C:\Users\nikos7\Desktop\files\file2.txt
C:\Users\nikos7\Desktop\files\file3.txt
C:\Users\nikos7\Desktop\files\file4.txt
C:\Users\nikos7\Desktop\files\file5.txt

This was an example on how to list files with certain extension only using FilenameFilter in Java.