Question

281~name~location~@time@room%
@time2@room2%
@time3@room3;
I need to delete the second line after the % in text file. But i dont know how to do that.

Answer 1

BufferedReader in = null;
out = null;
File sdCard = Environment.getExternalStorageDirectory();
File root = new File (sdCard.getAbsolutePath() + "/yourFile");
try {
        InputStream instream = new FileInputStream(file);
        in = new BufferedReader(new InputStreamReader(instream));
        out = new PrintWriter(new File(root,"yournewFile));

        String line; //a line in the file

    while ((line = in.readLine()) != null) {
            if (!Pattern.matches("^some pattern.*",line)) { //find the line we want to delete
                      //if it is not the line you want to delete then write it to new file
                            out.println(line);
            }

    }

    in.close();
    out.flush();
        out.close();
        File oldFile = new File (root,"/yourFile");
        oldFile.delete();
        File newFile = new File (root,"/yournewFile");
        newFile.renameTo(oldFile);
}catch(Exception e) {
    Toast.makeText(getApplicationContext(), e.toString(), Toast.LENGTH_SHORT).show();
}

You should read old file and match it to the line you want to delete.if it is not the line you want to delete then write it to another file.thus you will get the new file with only that line missing which you wanted to delete.
you are done.hope it will help.