Question

I have a program that loads lines from a user file, then selects the last part of the String (which would be an int)

Here’s the style it’s saved in:

nameOfValue = 0
nameOfValue2 = 0

and so on. I have selected the value for sure – I debugged it by printing. I just can’t seem to save it back in.

if(nameOfValue.equals(type)) {
        System.out.println(nameOfValue+" equals "+type);
            value.replace(value, Integer.toString(Integer.parseInt(value)+1));
        }

How would I resave it? I’ve tried bufferedwriter but it just erases everything in the file.

Answer 1

My suggestion is, save all the contents of the original file (either in memory or in a temporary file; I’ll do it in memory) and then write it again, including the modifications. I believe this would work:

public static void replaceSelected(File file, String type) throws IOException {

    // we need to store all the lines
    List<String> lines = new ArrayList<String>();

    // first, read the file and store the changes
    BufferedReader in = new BufferedReader(new FileReader(file));
    String line = in.readLine();
    while (line != null) {
        if (line.startsWith(type)) {
            String sValue = line.substring(line.indexOf('=')+1).trim();
            int nValue = Integer.parseInt(sValue);
            line = type + " = " + (nValue+1);
        }
        lines.add(line);
        line = in.readLine();
    }
    in.close();

    // now, write the file again with the changes
    PrintWriter out = new PrintWriter(file);
    for (String l : lines)
        out.println(l);
    out.close();

}

And you’d call the method like this, providing the File you want to modify and the name of the value you want to select:

replaceSelected(new File("test.txt"), "nameOfValue2");