Passing paintComponent to another class error

Question

I am trying to have each of the objects paint themselves into the JPanel by passing graphics through but i am getting a java.lang.NullPointerException error.

import java.awt.Color;
import java.awt.Graphics;
import javax.swing.JFrame;
import javax.swing.JPanel;
public class Main extends JPanel {
 private static final long serialVersionUID = 1L;
 Main panel;
 Player mainPlayer;
 public static void main(String[] args) {
 JFrame frame = new JFrame("Asteroids");
 frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
 Main panel = new Main();
 frame.add(panel);
 frame.setBackground(Color.BLACK);
 frame.setSize(500, 400);
 frame.setVisible(true);
 }
 public void paintComponent(Graphics g) {
 mainPlayer.paintComponent(g);
 }
}

And then this code is in a different .java file

import java.awt.Graphics;
public class Player {
 public Player() {
 }
 public void paintComponent(Graphics g) {
 }
}

Does anyone know why this code isn't working?

It is giving me:

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
 at Main.paintComponent(Main.java:23)

• MadProgrammer: Lets start with the fact that mainPlayer is not initalised any where in your code example
• semicolon: I do not feel very smart right now...
• Alex Fischer: Don't worry, it happens to the best of us.
• MadProgrammer: Welcome to the world of programming, where smart people are made to feel dumb ;)
• semicolon: Haha, I think i'm going to like it here.

Answer 1

You are not instantiating mainPlayer. Since the default value is null for uninstantiated object reference variables, you are getting a NullPointerException on line 23 when you are trying to dereference the variable.

• semicolon: Thanks, sorry for completely forgetting that

Answer 2

The mainPlayer variable is what is causing you problems. You should add in your main method, panel.mainPlayer = new Player(); Because mainPlayer is by default null, you will have to set it to some instance of an object in order to use it and call its methods.

• semicolon: I added mainPlayer = new Player() and made it static.