TestWCJava2.java

import java.io.BufferedOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.nio.MappedByteBuffer;
import java.nio.channels.FileChannel;
import java.util.Random;

public class TestWCJava2 {
    public static void main(String args[]) throws IOException {
        // generateFile();

        try {
            new TestWCJava2().run(args);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    private static void generateFile() throws IOException {
        Random r = new Random();
        byte[] buffer = new byte[1024];
        try (BufferedOutputStream bos = new BufferedOutputStream(new FileOutputStream("/tmp/three"))) {
            for (int i = 0; i < 15  * 1024; i++) {
                r.nextBytes(buffer);
                bos.write(buffer);
            }
        }
    }

    void run(String files[]) throws IOException {
        long t0 = System.nanoTime();
        wordCount("/tmp/three");
        long t1 = System.nanoTime();
        System.out.println("Elapsed time: " + (t1 - t0) / 1000 + "us");
    }
 
    int wordCount(String fileName) throws IOException {
        File f = new File(fileName);
        FileChannel fc = new FileInputStream(f).getChannel();
        MappedByteBuffer mem = fc.map(FileChannel.MapMode.READ_ONLY, 0, fc.size());
 
        int nlines = 0;
        byte newline = '\n';

        byte[] buffer = new byte[4096];

        while(mem.hasRemaining()) {
            int read = Math.min(mem.remaining(), buffer.length);
            mem.get(buffer);
            for (int i = 0; i < read; i++) {
                if (buffer[i] == newline) {
                    nlines++;
                }
            }
        }
 
        System.out.println(fileName + " lines: " + nlines);
 
        return nlines;
    }
}