Example of Anonymous Inner Classes

package com.bruceeckel;
 
//: c12:DirList2.java
//Uses anonymous inner classes.
//{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 DirList2 {
    public static FilenameFilter filter(final String regex) {
	// Creation of anonymous inner class:
	return new FilenameFilter() {
	    private Pattern pattern = Pattern.compile(regex);
 
	    public boolean accept(File dir, String name) {
		return pattern.matcher(new File(name).getName()).matches();
	    }
	}; // End of anonymous inner class
    }
 
    public static void main(String[] args) {
	File path = new File(".");
	String[] list;
	if (args.length == 0)
	    list = path.list();
	else
	    list = path.list(filter(args[0]));
	Arrays.sort(list, new AlphabeticComparator());
	for (int i = 0; i < list.length; i++)
	    System.out.println(list[i]);
    }
} // /:~

package com.bruceeckel;
 
//www.BruceEckel.com. See copyright notice in CopyRight.txt.
//modified by Code Panda; This class is used several times in those examples, so, move it into a public class.
import java.util.Comparator;
 
public 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());
    }
}