If-statement checking for filename correctness (appending ".txt") not working

Question

So I want to accept a file name from the user. I then want to check if the last four characters of the string are ".txt". If they aren't, append ".txt" to the end of the user inputted string. If they are, skip. Simple.

But it's not working - when I enter "exampledata.txt" it still adds ".txt" and throws a FileNotFoundException - and I can't figure out why. I've taken the same calculation and printed it out/verified in debugger; my method call to substring is correct.

Relevant code:

import java.util.*; 
import java.io.*;

public class MappingApp {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in); 
        String userInput;
        System.out.print("Enter file to read from: ");
        userInput = sc.nextLine();

        if ( (userInput.substring(userInput.length()-4, userInput.length())) != ".txt" ) {
            userInput += ".txt";
        }

        try {
            File f = new File(userInput);
            BufferedReader br = new BufferedReader(new FileReader(f));
        }
        catch (FileNotFoundException e) {
            System.err.println(e);
        }
    } 
}

You can simply use the Java String API's endsWith method to check if the userInput ends with ".txt" or not. — Naveen Kumar, Apr 08 '17 at 04:07

score 0 · Answer 1 · answered Apr 08 '17 at 04:13

0

Usually you don't compare strings as != or == Try changing

if ( (userInput.substring(userInput.length()-4, userInput.length())) != ".txt" )

to

if ( !(userInput.substring(userInput.length()-4, userInput.length()).equals (".txt") )

Hope this will help.

answered Apr 08 '17 at 04:13

Mithun Adhikari

521
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If-statement checking for filename correctness (appending ".txt") not working

1 Answers1