What does it mean: JavaFX application class must extend javafx.application.Application?

What is meant by this error:

Error: Main method not found in class Static.A, please define the main method as: public static void main(String[] args) or a JavaFX application class must extend javafx.application.Application

I was trying to run a program Without main Method..

public class A
{
    static
    {
      System.out.println("Hello");
      System.exit(0);
     }
}