DouKaku?

import java.io.*;

public class Tail {
    private static final int MAX_LINE_LENGTH = 1000;
    private static final long SLEEP_TIME = 500; // 500 m sec
    private static int numOfLine = 10;
    private static boolean fOption = false;
    private static String fileName = null;
    private static InputStream targetStream = System.in;

    public static void main(String[] args) throws Exception {
        for (String s: args) {
            if ("-help".equals(s)) {
                System.err.println("Usage> java Tail [-f] [-<num>] [filename]");
                return;
            }
            else if ("-f".equals(s))
                fOption = true;
            else if (s.startsWith("-"))
                numOfLine = -Integer.parseInt(s);
            else
                fileName = s;
        }
        
        if (fileName != null) {
            File target = new File(fileName);
            long len = target.length();
            targetStream = new FileInputStream(target);
            len -= MAX_LINE_LENGTH * numOfLine;
            if (len > 0)
                targetStream.skip(len);
        }
        BufferedReader br = new BufferedReader(new InputStreamReader(targetStream));
        String line;
        String[] lines = new String[numOfLine];
        int ip = 0;
        while ((line = br.readLine()) != null) {
            lines[ip] = line;
            if (++ip >= numOfLine)
                ip = 0;
        }
        int i = ip;
        do {
            if (lines[i] != null)
                System.out.println(lines[i]);
            if (++i >= numOfLine)
                i = 0;
        } while (i != ip);
        if (fOption && fileName != null) {
            while (true) {
                Thread.sleep(SLEEP_TIME);
                line = br.readLine();
                if (line != null)
                    System.out.println(line);
            }
        }
    }
}