Main method not found in java?

Question

Java

package com.company;


public class QDemo2 {
    static double rootof2;
    static double rootof3;

    static {
        System.out.println("Внутри синтаксического блока QDemo2!");
        rootof2 = Math.sqrt(2.0);
        rootof3 = Math.sqrt(3.0);
    }

    QDemo2(String msg) {
        System.out.println(msg);
    }
}

    class SDemo3{
        public static  void main(String[] args){
            QDemo2 ob = new QDemo2("Внутри конструктора !");
            System.out.println("Корень квадратныйй из 2 равен" + QDemo2.rootof2);
            System.out.println("Корень из 3 " + QDemo2.rootof3);
        }
    }

As you can see, the Main method exists.
So what's the problem?

Answer 1

Make the SDemo3 class public!

Answer 2

There can be several classes in one java file, but one of them must be public. The class in which the static public method main is called must be public