When I Run My Code, I Get this Error:

Exception in thread "main" java.lang.NullPointerException

at Main.drawBlock(Main.java:48)
at Main.<init>(Main.java:43)
at Main.main(Main.java:58)

I Think this is Because of The Graphics that I Drew, But That Never Happened Before. I Have No Idea WHY. Here is My Code:

Graphics2D g;
static JFrame jf = new JFrame();
Image Air;
Image Grass;
Image icon;

public Main() {
    icon = new ImageIcon(this.getClass().getResource("Icon.png")).getImage();
    Grass = new ImageIcon(this.getClass().getResource("Grass.png")).getImage();
    Air = new ImageIcon(this.getClass().getResource("Air.png")).getImage();

    jf.setIconImage(icon);
    drawBlock(Air,0,0);

}

private void drawBlock(Image img, int x, int y) {
    g.drawImage(img,x,y,null);
}

public static void main(String[] args) {
    jf.setSize(792,528);
    jf.setLocationRelativeTo(null);
    jf.setDefaultCloseOperation(jf.EXIT_ON_CLOSE);
    jf.setVisible(true);
    jf.setTitle("Minecraft 2D Adventure");

    new Main();

}}

Because you have not initialized Graphics2D g so g is null

The real Reason of NPE is Graphics2D is a AbstractClass and you can not instantiate it.

You can create instance of Graphics2D instance like below

GraphicsEnvironment env =
        GraphicsEnvironment.getLocalGraphicsEnvironment();
 env.createGraphics(BufferedImage);

or you can use createGraphics() From BufferedImage

public Graphics2D createGraphics()

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