How can I get the count of line in a file in an efficient way? [duplicate]

Question

I have a big file. It includes approximately 3.000-20.000 lines. How can I get the total count of lines in the file using Java?

Answer 1

BufferedReader reader = new BufferedReader(new FileReader("file.txt")); int lines = 0; while (reader.readLine() != null) lines++; reader.close(); 

Update: To answer the performance-question raised here, I made a measurement. First thing: 20.000 lines are too few, to get the program running for a noticeable time. I created a text-file with 5 million lines. This solution (started with java without parameters like -server or -XX-options) needed around 11 seconds on my box. The same with wc -l (UNIX command-line-tool to count lines), 11 seconds. The solution reading every single character and looking for '\n' needed 104 seconds, 9-10 times as much.

Answer 2

Files.lines

Java 8+ has a nice and short way using NIO using Files.lines. Note that you have to close the stream using try-with-resources:

long lineCount; try (Stream<String> stream = Files.lines(path, StandardCharsets.UTF_8)) {   lineCount = stream.count(); } 

If you don't specify the character encoding, the default one used is UTF-8. You may specify an alternate encoding to match your particular data file as shown in the example above.