Static variable error in main function

Question

Dont know why it would be doing this. It is bascially telling me that every class I call in my main function needs to be static which is crazy.
import javax.swing.*;
import java.awt.*;
class Frame extends JFrame
     public Frame()
          setTitle("My Empty Frame");
          setSize(300,200);
          setLocation(10,200);
          this.show();
public class Main extends JFrame
     public JFrame frame;
     public Main()
          frame = new JFrame();
     public static void main(String[] args)
          System.out.println("CS348 Project 1");
          frame.setVisible(true); <--------------------ERROR
}Thanks for the help.

Answer 1

The problem (basically), is that you could do the following if you felt like it:
import javax.swing.*;
import java.awt.*;
class Frame extends JFrame
     public Frame()
          setTitle("My Empty Frame");
          setSize(300,200);
          setLocation(10,200);
          this.show();
public class Main extends JFrame
     public JFrame frame;
     public Main()
          frame = new JFrame();
     public static void main(String[] args)
          Main main1 = new Main();
          Main main2 = new Main();
          Main main3 = new Main();
          //what frame is this talking about??
          frame.setVisible(true); <--------------------ERROR
}What you would want instead is probably something like this:
Main main1 = new Main();
main1.getFrame().setVisible(true);This leads to a few other questions: why are you extending JFrame if you have a JFrame variable in the class? Does that class have a JFrame, or is it a JFrame? You should almost definitely go with the "have" answer.