delete first 1000 lines from text file

Question

I have a file have lot of records in millions. here I want to read first 2000 records and delete them after read. i am able to read record but please let me know how to delete.

public class Files {


    public static void files(int index) throws IOException {
        try {

            //numbers num = new numbers();
            BufferedReader br = null;
            BufferedWriter bw = null;
            try {

                String sCurrentLine = "";
                br = new BufferedReader(new FileReader("data.txt"));
                bw = new BufferedWriter(new FileWriter("File_2.txt"));

                int i = 0;
                while ((sCurrentLine = br.readLine()) != null && i < index) {
                    System.out.println(++i + " " + sCurrentLine);
                    bw.write(sCurrentLine);
                    bw.write(System.getProperty("line.separator"));
                    //sCurrentLine = br.readLine();
                }

            } catch (IOException e) {
                e.printStackTrace();
            } finally {
                try {
                    br.close();
                    bw.close();
                    if (br != null) {
                        br.close();
                    }
                } catch (IOException ex) {
                    ex.printStackTrace();
                }
            }

        } catch (Exception e) {

        }
    }

}

possible duplicate of http://stackoverflow.com/questions/1377279/find-a-line-in-a-file-and-remove-it — ingrid.e, Mar 24 '16 at 11:32
You could create a temporary file which contains the lines 2000+ till the end and replace the original file later by this temporary file. — SubOptimal, Mar 24 '16 at 11:39
You can't delete from the original file, you can only copy the lines you want to another file and delete the current one and rename the new file as your current file. — user3437460, Mar 24 '16 at 11:49

score 0 · Answer 1 · answered Mar 24 '16 at 11:50

You have several options: If you want to update the existing file - read and write at the same time, you will need a RandomAccessFile stream. With that you can open file for both - reading and writing. On the other hand, it might be risky to update the same file without keeping original, as your application might crash at some point and you will be left with a damaged file.

Another way would be take a new temporary file and write the part you'd like to keep in that file, but if you have millions of records, this might not be efficient.

delete first 1000 lines from text file

1 Answers1