As you do not now where the 3rd line begins you can not jump to there and read only the line, so you have to waste time and read all the lines before you get to the requested one...
This code will do the job, but consider to re-design your application as the code will be very inefficient when the file grows large...
BufferedReader oBuffer = new BufferedReader(new FileReader(szPath))) {
String szLine;
int nCount = 0;
while ((szLine = oBuffer.readLine()) != null) {
nCount++;
if(nCount > 3) break;
}