How to Get File Extension in Java - RameshMF/java-io-guide GitHub Wiki

In this example, we will check the file extensions such as txt, docx,pdf etc.

Get File Extension Example

1. Let's use lastIndexOf() method of String class to find the index of last character ".".
2. First check whether the file has extention or not.
3. Use substring() method to get extension of the file.

package com.javaguides.javaio.fileoperations.fileexamples;

import java.io.File;

/**
 * This Java program demonstrates how to get file extension in Java example.
 * @author javaguides.net
 */

public class GetFileExtensionExample {
	private static String getFileExtension(File file) {
		String fileName = file.getName();
		if (fileName.lastIndexOf('.') != -1 && fileName.lastIndexOf('.') != 0) {
			return fileName.substring(fileName.lastIndexOf('.') + 1);
		} else {
			return "File don't have extension";
		}
	}

	public static void main(String[] args) {
		File file = new File("sample.txt");
		System.out.println(getFileExtension(file));
		
		File file1 = new File("sample");
		System.out.println(getFileExtension(file1));
		
		File file2 = new File("sample.docx");
		System.out.println(getFileExtension(file2));
		
	}

}

Output of the above program is:

txt
File don't have extension
docx

Reference

https://docs.oracle.com/javase/8/docs/api/java/io/File.html https://docs.oracle.com/javase/8/docs/api/java/lang/String.html