error could not find or load main class ubuntu code example

Example 1: Error: Could not find or load main class mina.calc.MinaCalculator in module mina

//You must change your class name

Example 2: Error: Could not find or load main class Hello Caused by: java.lang.ClassNotFoundException: Hello studio visual code

package dto;
/**
 * Simple Java program to demonstrate following error
 * Error :Could not find or load main class
 * 
 * @author Javin Paul
 */
public class HelloHP {

    public static void main(String args[]) {
        System.out.println("My first program in Java, HelloWorld !!");
       
    }

}