JFrame，JPanel和awt问题

Question

i am trying to make a simple java 2-d platformer. Java keeps giving me troubles some error "The serializable class Display does not declare a static final serialVersionUID field of type long" Can anybody help?

this is the error message I get when i try to run the program: http://i.imgur.com/H0Afv.png (on the website)

Here is the code:

import javax.swing.*;

public class Main {

    public static Display f;
    public static int width = 800;
    public static int height = 600;

    public static void main(String[] args)
    {

        f = new Display();
        f.setVisible(true);
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.setResizable(true);
        f.setSize(width, height);
        f.setLocationRelativeTo(null);
        f.setTitle("2-D Platformer");
    }


}

//This is my display class.

import java.awt.*;

import javax.swing.*;

/* this is where the error is
 *
 */           V 
public class Display extends JFrame{

    public Display p;
    public Display()
    {

        p = new Display();
        add(p);
        setLayout(new GridLayout(1, 1, 0 , 0));
    }
}

//and this is my display2 class
import java.awt.Color;

import javax.swing.*;

/* this is where the error is
 *too
 */            V 
public class Display2 extends JPanel{

    public Display2()
    {
        setBackground(Color.BLACK);
    }
}

Answer 1

It's not an error, it's a warning and it comes from your extending a serializable class (one of the GUI components that your class is extending) and not giving it final serialVersionUID field as the Serializable interface contract stipulates. This is not really important since it is very unlikely that you'll want to serialize objects of this class (store them to disk or transmit them), and so you can either safely ignore this warning or use an annotation, @SuppressWarnings(“serial”) , to tell the compiler to ignore it. ie,

Edit: or you can give it a default serialVersionUID as bhuang3 states. 1+ to his answer!

Edit 2:

@SuppressWarnings(“serial”)
public class Display extends JFrame {

   // .....

}

Edit 3:
Next we'll discuss why it's usually not necessary and in fact often not a good idea to create classes that extend JFrame or other components unless you are overriding some of the methods of the super class...

Answer 2

I think you need to declare a serialVersionUID in your Display2 class. for example: private static final long serialVersionUID = 1L;