[OS] Lab 01 - Problem 1

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

public class HW01_1 {
    public static void main(String [] args) {
        if(args.length != 0) {

            File f = new File(args[0]);

            File [] files = null;

            if(f.isDirectory()) {
                    files = f.listFiles(new DirFilter(".txt"));
            }

            long length = 0;

            if(files != null) for(File file : files) length += file.length();

            System.out.println(length / files.length);
        }
    }
}

class DirFilter implements FilenameFilter
{
    private String filter;

    DirFilter(String filter) {
        this.filter = filter;
    }

    @Override
    public boolean accept(File dir, String name) {
        String tmp = new File(name).getName();
        return tmp.contains(filter);
    }
}