Replacing a line in a file from Scanner

Question

I am having a a bit of trouble trying to replace a line in a text file with the user input. Whenever I try to replace the line all other lines in the text file gets deleted. Can anyone assist me with this issue?

     public static void removedata(String s) throws IOException {

    File f = new File("data.txt");
    File f1 = new File("data2.txt");
    BufferedReader input = new BufferedReader(new InputStreamReader(
            System.in));
    BufferedReader br = new BufferedReader(new FileReader(f));
    PrintWriter pr = new PrintWriter(f1);
    String line;

    while ((line = br.readLine()) != null) {
        if (line.contains(s)) {

            System.out
                    .println("I see you are trying to update some information... Shall I go ahead?");
            String go = input.readLine();
            if (go.equals("yes")) {
                System.out.println("Enter new Text :");
                String newText = input.readLine();
                line = newText;
                System.out.println("Thank you, Have a good Day!");
                break;
            }
            if (go.equals("no")) {

                System.out.println(line);
                System.out.println("Have a good day!");
                break;
            }
        }

        pr.println(line);
    }
    br.close();
    pr.close();
    input.close();
    Files.move(f1.toPath(), f.toPath(), StandardCopyOption.REPLACE_EXISTING);

}

And here is my main

public static void main(String args[]) throws ParseException, IOException {
    /* Initialization */


    String[] keywords = { "day", "month" };
    Scanner in = new Scanner(System.in);
    Scanner scanner = new Scanner(System.in);
    String input = null;

    System.out.println("Welcome");
    System.out.println("What would you like to know?");

    System.out.print("> ");
    input = scanner.nextLine().toLowerCase();           

    for (int i = 0; i < keywords.length; i++) {



          if (input.contains(keywords[i])) {

          removedata(keywords[i]);
          }
    }

   }

And my textfile contains " the day is tuesday" and "the month is march". Aassuming the user enters "the day is wednesday" I want to replace the old line with the new line. Any suggestions?

You can't directly replace a line from a text file. You have rewrite the entire file. — But I'm Not A Wrapper Class, Apr 27 '15 at 19:39
Your answer already given in http://stackoverflow.com/questions/20039980/java-replace-line-in-text-file ? — Shervin, Apr 27 '15 at 19:40
Instead of saying newText = line...have you tried `replace()`? Also, I'm certain you have to read the file, and then write the entire file — freddiev4, Apr 27 '15 at 19:42

score 1 · Accepted Answer · answered Apr 27 '15 at 19:46

To replace text in a text file , you need to have a temporary file where you store the modified text . I think you actually did that by using f and f1 .But you used break; inside that while loop , so once the line is replaced and printed the loop stops . I think all you have to do is remove that break;

MadConan · Answer 2 · 2015-04-27T20:01:15.020

You have two options

Read the file as usual until you get to the line you are looking for, being sure to write all lines to some temp file. Write the new line to the temp file, and then continue the operation. Now replace the old file with the new file.

private void updateFile(String lineToFind, String lineToUse, File f) throws IOException{
File tempFile = new File(f.getAbsolutePath()+".tmp");
try(BufferedReader reader = new BufferedReader(new FileReader(f));
PrintWriter writer = new PrintWriter(new FileWriter(tempFile))) {
    String line;
    while ((line = reader.readLine()) != null) {
        if (line.equals(lineToFind)) {
            writer.println(lineToUse);
        } else {
            writer.println(line);
        }
    }
}
f.delete();
tempFile.renameTo(f);
}

Use a RandomAccessFile to manipulate the file contents. This is far more complicated and probably not worth the effort, but it is an option.

Option 1 is what OP is currently doing ... or tries to do. – Tom Apr 27 '15 at 20:08 — Tom, Apr 27 '15 at 20:08

Replacing a line in a file from Scanner

2 Answers2