如何把a目录下面的文件批量修改名称

import java.io.File;

public class ChangeFileName {
    public static void main(String[] args) {

        String orgFileStr = "D:/迅雷下载/aaa";
        String str = "a";
        File orgFile = new File(orgFileStr);
        File[] files = orgFile.listFiles();
        Integer num = 1;
        for (File file : files) {
            if (file.isFile()) {
                System.out.println(file.getName());
                String newName = str + num + ".mp4";

                File fileNew = new File(orgFile, newName);
                file.renameTo(fileNew);
                num++;
            }
        }

        System.out.println("-----修改玩程！");

    }
}