Displays directory listing using regular expressions

// : c12:DirList.java
// Displays directory listing using regular expressions.
// {Args: "D.*\.java"}
// From 'Thinking in Java, 3rd ed.' (c) Bruce Eckel 2002
// www.BruceEckel.com. See copyright notice in CopyRight.txt.

import java.io.File;
import java.io.FilenameFilter;
import java.util.Arrays;
import java.util.Comparator;
import java.util.regex.Pattern;

public class DirList {
  public static void main(String[] args) {
    File path = new File(".");
    String[] list;
    if (args.length == 0)
      list = path.list();
    else
      list = path.list(new DirFilter(args[0]));
    Arrays.sort(list, new AlphabeticComparator());
    for (int i = 0; i < list.length; i++)
      System.out.println(list[i]);
  }
}

class DirFilter implements FilenameFilter {
  private Pattern pattern;

  public DirFilter(String regex) {
    pattern = Pattern.compile(regex);
  }

  public boolean accept(File dir, String name) {
    // Strip path information, search for regex:
    return pattern.matcher(new File(name).getName()).matches();
  }
} ///:~

class AlphabeticComparator implements Comparator {
  public int compare(Object o1, Object o2) {
    String s1 = (String) o1;
    String s2 = (String) o2;
    return s1.toLowerCase().compareTo(s2.toLowerCase());
  }
} ///:~