Question

I understand how to search through a txt file searching for a value (or an id in this case) however usually this returns the first option it finds.

How would I work this so that it finds the last value in the file related to the id and uses that one? (in this case, the card ID of 17 has a balance of 813.

txt file example

17,721.0
17,744.0
17,767.0
17,790.0
17,813.0

my current search code.

public static double readBalance(int cardNumber)
{
  double balance;  
  String line;

  try {
        File CbFile = new File("cardBalance.txt");
        BufferedReader br = new BufferedReader(
                            new InputStreamReader(
                            new FileInputStream(CbFile)));

        while((line = br.readLine()) != null) {
            if(line.indexOf(cardNumber) != -1)
                break;
        }
        String[] s = line.split("\\,");

        balance = Double.parseDouble(s[1]);
        System.out.println("Blalance of " + cardNumber +
                           " is: " + s[1]);
        br.close();
    } catch(IOException e) {
        System.out.println("read error: " + e.getMessage());
    }


  return  balance;

}

Answer 1

lastIndexOf(String) will give you the last occurrence of a String, if you can read the entire file into memory at once.

If not, you’ll want something like:

String cardInfo;
String cardNumberString = cardNumber + ","; // makes sure that you don't get your
                                            // id in the middle of a value
while((line = br.readLine()) != null) {
    if(line.indexOf(cardNumberString) != -1)
        cardInfo = line;
}