一、单层多个

代码实现如下：

public class Main {
    public static void main(String[] args) {
        //在D盘中创建
        File file = new File("D:"+File.separator+"docum");
        file.mkdir();
        //在D盘中的docum目录中创建
        file = new File("D:\\docum"+ File.separator+"C");
        file.mkdir();
        file = new File("D:\\docum"+ File.separator+"java");
        file.mkdir();
        file = new File("D:\\docum"+ File.separator+"python");
        file.mkdir();
    }
}

二、多层单个

public class Main {
    public static void main(String[] args) {
        File file = new File("D:"+File.separator+"One"
                                +File.separator+"Two"
                                +File.separator+"Three");
        file.mkdirs();
    }
}

三、多层多个

public class Lx02 {
    public static void main(String[] args) {
        File file = new File("D:"+File.separator+"One"
                                +File.separator+"Two"
                                +File.separator+"Three");
        file.mkdirs();
        file = new File("D:\\One\\Two"+ File.separator+"a"+ File.separator+"b");
        file.mkdirs();
    }
}