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Java File Class File[] listFiles(FilenameFilter fnf) method with Example

Java File Class File[] listFiles(FilenameFilter fnf) method: Here, we are going to learn about the File[] listFiles(FilenameFilter fnf) method of File class with its syntax and example.
Submitted by Preeti Jain, on July 10, 2019

File Class File[] listFiles(FilenameFilter fnf)

  • This method is available in package java.io.File.listFiles(FilenameFilter fnf).
  • This method is used to return the names of all the files in the form of an array of files which is represented in the filepath.
  • The return type of this method is File[] i.e. It returns an array of files or directories which is represented in filepath if a given path is directory else return null.
  • This method may raise an exception( i.e. Security Exception) if the write access is not given to the file.
  • This method is overridable. The first method does not accept any parameter and the second method accept one parameter and Third method is also accept one parameter.

Syntax:

    File[] listFiles(FilenameFilter fnf){
    }

Parameter(s):

We pass only one object FilenameFilter as a parameter in the method and with the help of this argument, we can find files with filter(i.e we can find specific files).

Return value:

The return type of this method is File[] i.e. it returns all file names in an array of the file which is represented in a filepath.

Java program to demonstrate example of listFiles() method

// import the File class because we will use File class methods
import java.io.*;

// import the Exception class because it may raise an exception 
// when working with files
import java.lang.Exception;

public class ToListSpecificFiles {
    public static void main(String[] args) {
        try {
            // Specify the path of file and we use double slashes to 
            // escape '\' character sequence for windows otherwise 
            // it will be considerable as url.
            File file = new File("C:\\Users\\computer clinic\\OneDrive\\Articles");

            // Create a FilenameFilter object
            FilenameFilter fnf = new FilenameFilter() {

                public boolean accept(File file, String name) {
                    return name.startsWith("H");
                }
            };
            // By using list(fnf) returns all the files and directories 
            // which is represented in a file path if file path is a 
            // directory and all file or directories starts with 'J'.

            File[] filelist = file.listFiles(fnf);

            System.out.println("These are the name of files represented in a given directory whose name starts with H :" + file.getPath());

            // By using loop to traverse the filenames 
            // and directories in the given path .
            for (int i = 0; i < filelist.length; i++)
                System.out.println(filelist[i].getName());

        } catch (Exception e) {
            System.out.println("An error occurred.");
            e.printStackTrace();
        }
    }
}

Output

D:\Programs>javac ToListSpecificFiles.java

D:\Programs>java ToListSpecificFiles
These are the name of files represented in a given directory whose name starts with H:C:\Users\computer clinic\OneDrive\Articles
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