java: how to use bufferedreader to read specific line

Lets say I have a text file called: data.txt (contains 2000 lines)

How do I read given specific line from: 500-1500 and then 1500-2000 and display the output of specific line?

this code will read whole files (2000 line)

public static String getContents(File aFile) {

        StringBuffer contents = new StringBuffer();

        try {

        BufferedReader input = new BufferedReader(new FileReader(aFile));
        try {
            String line = null; 

            while (( line = input.readLine()) != null){
            contents.append(line);
            contents.append(System.getProperty("line.separator"));
            }
        }
        finally {
            input.close();
        }
        }
            catch (IOException ex){
            ex.printStackTrace();
        }

        return contents.toString();
}

How do I modify above code to read specific line?