balance.txt

//Method 1
InputStreamReader ir=new InputStreamReader(System.in);
        BufferedReader br=new BufferedReader(ir);
        FileInputStream f=new FileInputStream("balance.txt");
        File file=new File("balance.txt");
        char[] cur_bal=new char[(int) file.length()];
        int i=f.read(),t=0;
        System.out.println("Enter the amount u want to deposit");
        int dep_amt=Integer.parseInt(br.readLine());
        while(i!=-1){
            cur_bal[t++]=(char)i;
            i=f.read();
        }
        int cur_bal2=Integer.parseInt(String.valueOf(cur_bal));
        cur_bal2+=dep_amt;
        f.close();
        FileOutputStream fo=new FileOutputStream("balance.txt");
        byte[] b=(String.valueOf(cur_bal2)).getBytes();
        fo.write(b);
        System.out.println("Amount successfully deposited.");
        fo.close();

//Method 2
Scanner sc=new Scanner(System.in);
        System.out.println("Enter the deposit Amount");
        int deposit_amount=sc.nextInt();

        Scanner sc1=new Scanner(new File("balance.txt"));
        int cur_balance=sc1.nextInt();

        cur_balance+=deposit_amount;

        FileOutputStream f=new FileOutputStream("balance.txt");
        String s=Integer.toString(cur_balance);
        byte[] b=s.getBytes();
        f.write(b);
        f.close();