I use huge data files, sometimes I only need to know the number of lines in these files, usually I open them up and read them line by line until I reach the end of the file<
The answer with the method count() above gave me line miscounts if a file didn't have a newline at the end of the file - it failed to count the last line in the file.
This method works better for me:
public int countLines(String filename) throws IOException {
LineNumberReader reader = new LineNumberReader(new FileReader(filename));
int cnt = 0;
String lineRead = "";
while ((lineRead = reader.readLine()) != null) {}
cnt = reader.getLineNumber();
reader.close();
return cnt;
}