How to get the extension of a file using Java

Submitted by donbermoy on Monday, May 26, 2014 - 23:23.
Today, I will teach you how to create a program that get the extension of a file using java. For example if we input a text file of .txt file extension then the output will be .txt. So, now let's start this tutorial! 1. Open JCreator or NetBeans and make a java program with a file name of extensionFile.java. 2. Import java.io package. Hence we will use an input/output in creating files. 
  1. import java.io.*;
3. Also in your program, create a variable for the separator as it will separate the extension file of dot(.). Make this as a public static String variable. 
  1.   public static  String separator = ".";;
4. To get the extension of a file we will create a method named getFileExtension with a File paramater as String. If the file inputted is empty, then it will return as null. 
  1.     public static String getFileExtension(File file) {
  2.         if (file == null) {
  3.             return null;
  4.         }
Separate the file name and the file extension. 
  1.         String extName = file.getName();
  2.         int extIndex = extName.lastIndexOf(extensionFile.separator);
  3.  
  4.         if (extIndex == -1) {
  5.             return "";
  6.         } else {
  7.             return extName.substring(extIndex + 1);
  8.         }
5. In your main, instantiate the File class having the file variable. For example you want to have a file name of data.docx, READ FIRST.txt, extensionFile.java, and extensionFile.class. Note: you can change the file name of this file. 
  1.         File file = new File("data.docx");
  2.         String extension = extensionFile.getFileExtension(file);
  3.         System.out.println("Extension of the File is: " + extension + " of " + file);
  4.  
  5.         file = new File("READ FIRST.txt");
  6.         extension = extensionFile.getFileExtension(file);
  7.       System.out.println("Extension of the File is: " + extension + " of " + file);
  8.  
  9.        file = new File("extensionFile.java");
  10.         extension = extensionFile.getFileExtension(file);
  11.         System.out.println("Extension of the File is: " + extension + " of " + file);
  12.  
  13.       file = new File("extensionFile.class");
  14.         extension = extensionFile.getFileExtension(file);
  15.      System.out.println("Extension of the File is: " + extension + " of " + file);
To get the extension of the file, i simply use the getFileExtension method that we have created earlier with the extensionFile class and its inputed file. Then, we displayed the output using System.out.println(). Output: output Hope this helps! :) Best Regards, Engr. Lyndon Bermoy IT Instructor/System Developer/Android Developer/Freelance Programmer If you have some queries, feel free to contact the number or e-mail below. Mobile: 09488225971 Landline: 826-9296 E-mail:[email protected] Add and Follow me on Facebook: https://www.facebook.com/donzzsky Visit and like my page on Facebook at: https://www.facebook.com/BermzISware

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