Replacing each line of a file

Hello,
i have this txt file with a layout like this

Code:

---

50 - 3
52 - 8
53 - 35
54 - 14
56 - 23
58 - 45
60 - 28
62 - 89
64 - 57
66 - 466
68 - 167
70 - 1271
72 - 782

---

i want to keep only the first number (before the " - ") on each line of the file.
How can i do this using bufferedreader and bufferedwriter? I was thinking about getting the indexOf the " - " and then using the substring method to remove the rest of the line but i mess up somehow...

Thanks for your time :)

Hello.

Your idea is tottaly okey.

Here is simple example:

Code:

---

public static void main(String [] args)
{
        // read every line
        String input = "50 - 3";

        //find position of " -"  {space}-
        int position = input.indexOf(" -");

        //use substring
        String firstNumber = input.substring(0, position);

        System.out.println(firstNumber);

}

---

Just read line and get your numbers :) ( HINT: google: java file read every line )

I hope it will help u.

Have fun :)

this is my code currently:

Code:

---

        public static void originalDumpReplacer() throws IOException {
                BufferedReader reader = new BufferedReader(new FileReader("dump2.txt"));
                int lines = 0;
                while (reader.readLine() != null) {
                        lines++;
                }
                System.out.println("Item count to be dumped: " + lines);
                System.out.println("Now replacing the original Dump...");
                BufferedWriter writer = new BufferedWriter(
                                new FileWriter("dump2new.txt", true));
                for (int i = 0; i < lines; i++) {
                        String nextLine = reader.readLine();
                        int position = nextLine.indexOf(" - ");
                        String firstNumber = nextLine.substring(0, position);
                        writer.write(firstNumber);
                        writer.newLine();
                        writer.flush();
                }
                writer.close();
                reader.close();
        }

---

I end up with a NullPointerException at int position = nextLine.indexOf(" - ");
and an empty txt file (dump2new.txt)
:=-:

Hello.

Fast look on your code:



in while loop your reader reached till EOF.

from link: bla bla returns null if the end of the stream has been reached

Think about it :)

Best solution, place breakpoint line before int position = nextline.... and debug it :)

Oh thanks, i understand more about how bufferedreader and bufferedwriter work now!
Added a second reader and everything went like a charm.
Thanks alot for your time :(nod):

You only actually need the one reader, and a single loop.
Simply read a line, process it (ie get the part of the string you want) and write that out.

Code:

---

String line;
while ((line = reader.readLine()) != null) {
  write substring line.
}

---