Java: Bank simulation: Write to file, erased text/writing symbols

As a way to learn java, I attempted to write something simulating a bank(adding or removing numbers). I succeeded in creating a file(if one does not exist already), and then read from it, but when I attempt to write to it, it fails. I started with FileWriter, where it just erased the text in the document(balance.txt). I then tried BufferedWriter, and it wrote to the document, but it was just symbols instead of actual text/numbers. I’m aware that I’m a newbie when it comes to coding, but is there a solution to this? Thank you.

if (choice.equals("ADD")){
            System.out.println("Currently selected: " + choice);
            //write to file
            try {
                String filePath = "C:\Users\user\Desktop\programming\projects\java\RandomStuff\Bank\balance.txt";
            //    System.out.println("How much would you like to add?");
            //    Scanner inputAdd = new Scanner(System.in);
            //    String balanceToAdd = inputAdd.nextLine();
            //    writeToFile.write(balanceToAdd);



                int balanceToAdd = 1;
                BufferedWriter out = new BufferedWriter(new FileWriter(filePath));
                out.write(balanceToAdd);
                out.close();
                System.out.println("Added: " + balanceToAdd);
            }   //try end
            catch(IOException e){
                System.out.println("Error(line56): " + e.getMessage());
            }

Answer

public FileWriter(String fileName, boolean append)

I think you should use append to edit your file.

 BufferedWriter out = new BufferedWriter(new FileWriter(filePath,true));