stream -->demo1 DirList

package stream.demo1;

import java.io.File;
import java.io.FilenameFilter;
import java.util.Arrays;
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, String.CASE_INSENSITIVE_ORDER);
        for (String dirItem : list)
        {
            System.out.println(dirItem);
        }
    }
}

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