How to run a java .class file that extends a Class which is in another directory?

Question

I first met this problem in my Ideas, I wrote a Class that extends javax.servlet.http.HttpServlet, My Ideas throws an error message reads Error: Could not find or load main class com.bjpowernode.OneServlet, here is the image: enter image description here

It can be seen that Idea didn't show the red wavy line, that shows my codes are fine. I found a solution to this problem from enter link description here, I changed the scope from provided to compile: enter image description here But I actually want to know why and how it works? I compared the difference of Idea compilation instructions under different scope setting，I found that when Idea uses java command to run the .Class, the parameter -classpath of the command of the compile scope has two more paths: D:\apache-tomcat-8.0.50\lib\jsp-api.jar;D:\apache-tomcat-8.0.50\lib\servlet-api.jar That's to say, Idea didn't consider external library paths when run .class under the provided scope, and the super Class HttpServlet is from servlet-api.jar package. Why? To simplify the problem, I created two different classes under two different paths and packages: Class Base and Class Sub, and Sub extends Base. The codes of the Base is here:

package base;
public class Base{
    public static void main(String[] args) {
    
    }
}

The codes of the Sub is here:

package sub;
import base.Base;
public class Sub extends Base{
    public static void main(String[] args) {
        System.out.println("In Sub");
    }
}

The path of Base is ./path1/base/Base.java and the path of Sub is ./path2/sub/Sub.java. I compiled them using these two commands:

javac ./path1/base/Base.java -d ./path1
javac ./path2/sub/Sub.java   -d ./path2  -cp "./path1;./path2"

And compiled successfully. But when I run sub.Sub using the command below:

java sub.Sub -cp "./path1;./path2"

And I got the same error:

Error: Could not find or load main class sub.Sub

Ive tried multiple variations of this, but none of them seem to work. Any ideas? Although I solved the problem of idea reporting errors, I still could not understand the principle behind? I hope this question can help me to figure it out. My jdk version is 1.8. Thanks in advance.