# Java: Example - Display Extension

This program reads in a file name and displays the extension (that last part of the name after the final dot).

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    // Purpose: Display the extension (with .) of a file name.
    // File   : extension/FileExt.java
    // Author : Fred Swartz
    // Date   : 2005-09-06

    import javax.swing.*;

    public class FileExt {

        public static void main(String[] args) {
            //... Declare local variables.
            String fileName;   // The file name the user entered.
            String extension;  // The extension.

            //... Input a file name and remove whitespace.
            fileName = JOptionPane.showInputDialog(null, "Enter file name.");
            fileName = fileName.trim();

            //... Find the position of the last dot.  Get extension.
            int dotPos = fileName.lastIndexOf(".");
            extension = fileName.substring(dotPos);

            //... Output extension.
            JOptionPane.showMessageDialog(null, "Extension is " + extension);
        }
    }