多次读取包含相同条目的文件，但只想更改其中一个条目

Question

The BufferedReader is going through a file which contains various lines that all contain a specific identifier (so called qdr) . A qdr contains a specific amount. This amount can be reduced manually. When reducing the amount the BufferedReader goes through the file and checks for the lines that contain a specific qdr.

What it should do is to change that amount only in the first line it finds that contains that qdr and only if an amount is reduced that is bigger than the stated amount of a specific line (amount < 1), then it should reduce that amount from the next line that is identified by the same qdr.

I hope I could clarify my problems. Thank you very much for your help!

Via the bufferedreader it is being checked whether the file contains the given qdr. If it is the case it is adding the given amount to the one of the line. However, as you can see in the code, it is doing it to all the lines that contain that qdr. My idea would be to really go line by line with a loop and check whether each line is containing that qdr and if it is not the case then go to the next line, if it is the case see if the amount would be > 0 after altering with the new amount. If not, then look for the next line containing that qdr and do the same. Unfortunately, this is where I struggle.

  public static void removeDB(String qdr, int amount, String editor, String date) {            
  File readFile = new File(databaseRead);
  File writeFile = new File(databaseWrite);
  // creating the line variable to read through lines in while loop
  String line = null;
  // go through file
try {
    // create FileReader which reads the file
    FileReader fileReader = new FileReader(readFile);
    // wrap the FileReader into BufferedReader
    BufferedReader buffRead = new BufferedReader(fileReader);
    // FileWriter to write lines into new file
    FileWriter writer = new FileWriter(writeFile);
    BufferedWriter buffWrite = new BufferedWriter(writer);

    // go through all lines
    while ((line = buffRead.readLine()) != null) {

        if (line.contains(qdr)) {
        // set the amount 
        String blankSpaceAmount = clearOutput.split(", ")[3];
        // setting new Amount
        int remainingAmount = Integer.parseInt(blankSpaceAmount) - amount;

        // if amount is bigger than 0, show qdr in DB with new amount
        if (remainingAmount > 0) {
        // set the remaining Amount to String to show it in text field in Remove GUI
        remAmount = String.valueOf(remainingAmount);
        // read line and replace the current amount String with remaining amount String
        String amountReplacement = line.replaceAll(blankSpaceAmount, remAmount);
        }

Answer 1

One thing you could do is use a boolean flag, to indicate that you have modified the first encountered qdr , perhaps name it qdrChanged . Declare it above your while loop and initialize it as false :

boolean qdrChanged = false;

then in the while loop:

// go through all lines
while ((line = buffRead.readLine()) != null) {
    if (line.contains(qdr) && !qdrChanged) {
        // set the amount but only if this hasn't been done already.
        String blankSpaceAmount = clearOutput.split(", ")[3];
        // setting new Amount
        int remainingAmount = Integer.parseInt(blankSpaceAmount) - amount;

        // if amount is bigger than 0, show qdr in DB with new amount
        if (remainingAmount > 0) {
            // set the remaining Amount to String to show it in text field in Remove GUI
            remAmount = String.valueOf(remainingAmount);
            // read line and replace the current amount String with remaining amount String
            String amountReplacement = line.replaceAll(blankSpaceAmount, remAmount);
        }
        // .... The rest of code for the: if (line.contains(qdr) && !qdrChanged) { code block .... 

        qdrChanged = true;  // Flag that qdr has been modified

    } // END of Code block for:  if (line.contains(qdr) && !qdrChanged) {      

    // The rest of your WHILE loop code
}     

Anyways, something to this effect.

Whatever you do, don't use break; to break out of the loop. This will also stop the write of your new file.

Before using Integer.parseInt() validate the string supplied to the method so as to avoid the possibility of a NumberFormatException :

/* If blankSpaceAmount is NOT a valid signed or unsigned
   integer value then make it a default value like 0 or 
   String.valueOf(amount) or whatever.
*/
if (!blankSpaceAmount.matches("-?\\d+") {
    blankSpaceAmount = "0";  // or throw a message or an exception if you like.
}  
int remainingAmount = Integer.parseInt(blankSpaceAmount) - amount;