Building the anonymous inner class in-place : Anonymous inner class « Class Definition « Java Tutorial

1. Java Tutorial
2. Class Definition
3. Anonymous inner class

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

public class MainClass {
  public static void main(final String[] args) {
    File path = new File(".");
    String[] list;
    if (args.length == 0)
      list = path.list();
    else
      list = path.list(new FilenameFilter() {
        private Pattern pattern = Pattern.compile(args[0]);

        public boolean accept(File dir, String name) {
          return pattern.matcher(new File(name).getName()).matches();
        }
      });
    Arrays.sort(list);
    for (int i = 0; i < list.length; i++)
      System.out.println(list[i]);
  }
}