クラスの簡略化暦[内部クラスから匿名内部クラスへ]

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 DirFileter(args[0]));
		
		Arrays.sort(list, String.CASE_INSENSITIVE_ORDER);
		for(String dirItem : list)
			System.out.println(dirItem);
	}
}

class DirFilter implements FilenameFlter
{
	private Pattern pattern;
	public DirFilter(String regex){
		pattern = Pattern.compile(regex);
	}
	public boolean accept(File dir, String name){
		return pattern.matcher(name).matches();
	}
}

public class DirList2 {
	
	public static FilenameFilter filter(final String regex){
		return new FilenameFilter(){
			private Pattern pattern = Pattern.compile(regex);
			public boolean accept(File dir, String name){
				return pattern.matcher(name).matches();
			}
		};
	}
	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, String.CASE_INSENSITIVE_ORDER);
		for(String dirItem : list)
			System.out.println(dirItem);
	}
}

public class DirList3 {
	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(name).matches();
				}
			});
		Arrays.sort(list, String.CASE_INSENSITIVE_ORDER);
		for(String dirItem : list)
			System.out.println(dirItem);
	}
}