String filepath       = "data.txt";
String newID          = textFId.getText()
String newRoadName    = textFRname.getText();
String newRoadNumber  = textFRnumber.getText();
String newCarType     = textFCartype.getText();

String tempFile = "datatemp.txt";
File oldFile = new File(filepath);
File newFile = new File(tempFile);
String ID         = "";
String RoadName   = "";
String RoadNumber = "";
String CarType    = "";

try {

 FileWriter     fw = new FileWriter(tempFile, true);
 BufferedWriter bw = new BufferedWriter(fw);
 PrintWriter    pw = new PrintWriter(bw);
 x = new Scanner(new File(filepath));
 x.useDelimiter("[,n]");
 while(x.hasNext()) {
 ID         = x.next();
 RoadName   = x.next();
 RoadNumber = x.next();
 CarType    = x.next();
 if(ID.equals(newID)) {
 System.out.println(newID);
 pw.println(newID + "," + newRoadName + "," + newRoadNumber + "," + newCarType);
 } else {
 pw.println(ID + "," + RoadName + "," + RoadNumber + "," + CarType);
 System.out.println(newID);
 }

 }
 x.close();
 pw.flush();
 pw.close();
 oldFile.delete();
 File dump = new File(filepath);
 newFile.renameTo(dump);
 }
 catch (Exception e3){
 System.out.println("UPDATE ERROR!!");
 }

1,PO,100,GB
2,PO,101,GB
3,PO,102,GB
4,PO,103,GB

1,PO,100,GB
2,PO,101,GB
3,PO,102,GB
4,PO,104,GB

4,PO,104,GB
4,PO,104,GB
4,PO,104,GB
4,PO,104,GB