How To Recursively Find Given String In A File

I have to recursively find a given string in a file. I HAVE to use the LineNumberReader class, and the output would be like so:

Line#Found : the string of the whole line

This is the code I've written:

public String findGivenString(String givenString, int currentLineNumber) {
LineNumberReader lnr = null;
try {
lnr = new LineNumberReader(new FileReader(getFile()), 4096);
lnr.setLineNumber(currentLineNumber);
String s = lnr.readLine().toLowerCase();

[Code] ....

I messed around with a bit, and it doesn't change to the new set line. Though the line number is incrementing! So it just keeps checking the first line of the file over and over again, which is why it can't find the given string. Which also throws the StackOverFlow exception I'm getting.

Here's the output if I remove the comment from the System.out...:

String @ that Line# 1: package banking;
String @ that Line# 2: package banking;
String @ that Line# 3: package banking;
String @ that Line# 4: package banking;
....

So you see it keeps checking the same line even though the line number IS incrementing.