Replacing each line of a file

[Elaforestis]

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

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 :)

[ContoNick]

Hello.

Your idea is tottaly okey.

Here is simple example:

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 :)

[Elaforestis]

this is my code currently:

	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)

[ContoNick]

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 :)

[Elaforestis]

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

[Tolls]

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.

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