覆盖Java txt文件中的一行

Question

So I have created this method which at the end displays the whole line because i am displaying the array after converting and editing it. So my Question is how can i know overwrite the array to the same line i grabbed it from. thanks in advance and here is my code.

       public void getData(String path, String accountNumber) {
    try {
        FileInputStream fis = new FileInputStream(path);
        BufferedReader br = new BufferedReader(new InputStreamReader(fis));

        System.out.println("Please Enter the Deposit amount That you would like to add.");

        Scanner sn = new Scanner (System.in);

         int add = sn.nextInt();

        String str;

        while ((str = br.readLine()) != null) {
            if (str.contains(accountNumber)) {
                String[] array = str.split(" ");
                int old = Integer.parseInt(array[3]);
                int Sum= old + add;
                String Sumf = Integer.toString(Sum);
                array[3] = Sumf;

                for (int i = 0; i < array.length; i++) {
                System.out.println(array[i]);}

                break;
            }
        }
    } catch (Exception ex) {
        System.out.println(ex);
    }


}

i am using string accountNumber to grab the specific line that i need. after getting the line i am changing it to an array while splitting the index with str.split(" "); . After that i know that i need to edit index number [3]. so i do so and then i put it back into the array. the final thing i need to do is to right the array back now.

Answer 1

You can keep track of the input from the file you are reading and write it back with the modified version.

public void getData(String path, String accountNumber) {
    try {
        FileInputStream fis = new FileInputStream(path);
        BufferedReader br = new BufferedReader(new InputStreamReader(fis));

        System.out.println("Please Enter the Deposit amount That you would like to add.");

        Scanner sn = new Scanner (System.in);

        int add = sn.nextInt();

        String line; // current line
        String input = ""; // overall input

        while ((line = br.readLine()) != null) {
            if (line.contains(accountNumber)) {
                String[] array = line.split(" ");
                int old = Integer.parseInt(array[3]);
                int Sum= old + add;
                String Sumf = Integer.toString(Sum);
                array[3] = Sumf;

                // rebuild the 'line' string with the modified value
                line = "";
                for (int i = 0; i < array.length; i++)
                    line+=array[i]+" ";
                line = line.substring(0,line.length()-1); // remove the final space
            }

            // add the 'line' string to the overall input
            input+=line+"\n";
        }

        // write the 'input' String with the replaced line OVER the same file
        FileOutputStream fileOut = new FileOutputStream(path);
        fileOut.write(input.getBytes());
        fileOut.close();
    } catch (Exception ex) {
        System.out.println(ex);
    }
}

Answer 2

This is how i understand the question that you have a file you will read it line by line and will make some changes and want to write it again at the same position. Create a new temp file and write the contents to the temp file, if changed write the changed result if not write it as it is. And at last rename the temp to your original file name