Exception in thread "AWT-EventQueue-1" java.lang.NullPointerException error

Question

i'm completely new to any sort or applet programming and my code is really rough. Currently i am making an applet that allows you to learn about different countries based on what continents they are in. It's really simple stuff but i am still struggling. Currently i am receiving the error

Exception in thread "AWT-EventQueue-1" java.lang.NullPointerException

at Culminating1.instructions1(Culminating1.java:69). This line is a simple g.setColor(Color.yellow);.

My codes really rough and needs a lot of work so any kind of help is appreciated.

Here is the rest of my code. Thanks a lot!

import java.applet.*;
import java.awt.*;
import javax.swing.*;
import javax.swing.JComponent;
import java.awt.Color.*;

public class Culminating1 extends Applet {

    private Image world, destination, globetrot, rice;

    private Button africa, americas, asia, europe, instructions, japan, china, qatar, uae,   thailand;
 private Graphics g = null;

    public void init() {

        this.setLayout(null);
        asia = new Button("Asia");
        africa = new Button("Africa");
        europe = new Button("Europe");
        americas = new Button("Americas");
        instructions = new Button("Instructions");
        add(asia);
        asia.setBounds(10, 120, 65, 25);
        add(africa);
        africa.setBounds(10, 190, 65, 25);
        add(americas);
        americas.setBounds(10, 260, 65, 25);
        europe.setBounds(10, 330, 65, 25);
        add(europe);
        instructions.setBounds(10, 410, 65, 25);

        add(instructions);
        world = getImage(getCodeBase(), "world.gif");
        destination = getImage(getCodeBase(), "Destination2.png");
        globetrot = getImage(getCodeBase(), "GlobeTrot.png");

    } // init method

     @Override
     public void paint(Graphics g)  
    {

        g.setColor(Color.orange);
        g.fillRect(0, 0, 1000, 1000);
        g.drawImage(world, 200, 100, 300, 300, this);
        g.drawImage(destination, 150, 425, 450, 80, this);
        g.drawImage(globetrot, 150, 10, 450, 80, this);

    } // paint method

    @Override
    public boolean action(Event e, Object o) {
        if (e.target == instructions) {
            instructions1();
        } else if (e.target == asia) {
            asia();
        }
        return false;
    }

     public void instructions1() {
        JFrame jp1 = new JFrame();
        Culminating1 a=new Culminating1 ();
        jp1.getContentPane().add(a, BorderLayout.CENTER);
        jp1.setSize(new Dimension(500,500));
        jp1.setVisible(true);

        g.setColor(Color.yellow);
        g.fillRect(0, 0, 1000, 1000);
        Font f;
        f = new Font("Broadway", Font.PLAIN, 20);
        g.setFont(f);
        g.setColor (Color.black);
        g.drawString("Welcome to Globe Trot!", 200, 20);
        g.drawString("In this game you will learn about countries around the world.", 200, 40);
        g.drawString("First choose an area of the world,", 200, 80);
        g.drawString("then at random a well known landscape will appear.", 200, 120);
        g.drawString("Your goal is to guess the country where the landscape is from.", 200, 160);
        g.drawString("If you are unable to guess after 10 seconds a flag will appear", 200, 200);
        g.drawString("from the same country. You have one minute to guess the country", 200, 240);
        g.drawString("before you move onto the next country. There are five in total", 200, 280);
    }

} // Test class

Answer 1

You state:

This line is a simple g.setColor(Color.yellow);.

Nothing simple about it. You set g to null on this line:

private Graphics g = null;

and then call a method on it, and so it should not come as a surprise that you're getting a NPE.

Solution:

• Don't call methods on variables set to null.
• Specifically for the Graphics object, don't use it outside of the painting methods except when Graphics objects extracted from images such as with BufferedImages.
• The Graphics parameter of the paint method is a parameter variable, and thus has a scope limited to the method only. It has no effect on the g field that you're using, and in fact shadows the field.

Also:

• You're better off creating Swing GUI's rather than AWT GUI's, unless you absolutely must create AWT Applets for a class.
• You seem to be trying to create a Swing JFrame inside of an AWT Applet which really doesn't make sense. What is the motivation behind this very unusual bit of code?
• If your intent is to create a Swing GUI, then don't have your class extend Applet, and don't have a paint method.
• If Swing, then you should have a class that extends JPanel and override its paintComponent(Graphics g) method and do all painting there.
• It's usually easier to show text in a JLabel or in a JTextComponent such as a JTextArea.

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Edit
You state in comment

Thanks for the advice i literally have no idea what i am doing but i want to use the graphics class outside of the paint method is there anyway i am able to do this or is it impossible.

It's possible but requires tricks.

• You could get the Graphics object from a BufferedImage and draw on it,
• but you're still then going to need to draw that BufferedImage in your paint (or again, better, a paintComponent(Graphics g) method of a JPanel.
• Again, if you're just posting text, you're better off not using a Graphics object at all, but instead using a component such as a JLabel, JTextField, JTextArea or something similar.
• A good simple tutorial on use of Swing Graphics can be found here: Lesson: Performing Custom Painting.
• A more in depth article can be found here: Painting in AWT and Swing

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Edit 2
Next comment:

So what i have is a basic intro screen and what i want to do is when the user clicks one of the buttons it takes them to another screen. I've been trying to use a method to do this.

I think that it would be better to either swap text in a text component, or swap JPanels using a CardLayout.

On the screen which they are being sent to after clicking the button there are graphics needed this is why i am trying to bring in the graphics class.

Again you could use a CardLayout, swap JPanels from the introduction JPanel to a display JPanel, and do your graphics in the display JPanel's paintComponent(Graphics g) method override.