Jpanel holding a Graphics2d object

Question

hi!
Im trying to properly extend JPanel to display a Graphics2d Object that already exists. So what I have done is extended JPanel, and in the constructor, I send the graphics2d object that i would like displayed on the jpanel object.
Then in paintComponent, I cast the graphics object to a graphics2d object and set the value equal to the graphics2d object already created.
The problem is that when I use the component, all I get is a blank jpanel. I dont know what the problem is... code follows, please let me know what you think
Thanks.
public class JPanelGraphics2d extends JPanel{
     Graphics2D m_g2d;
     JPanelGraphics2d (Graphics2D g){
          m_g2d = g;
          setPreferredSize(new Dimension(450, 450));
     public void paintComponent(Graphics g) {
          super.paintComponent(g);
          Graphics2D g2 = (Graphics2D)g;
          g2 = m_g2d;
}

Answer 1

It looks a bit like you don't understand the nature of Java's method parameters.
Setting g2 = m_g2d does nothing outside your paintComponent method - it simply changes the reference that g2 holds within your paintComponent.
However, there's also something else wrong about your approach. A Graphics object is simply a toolkit and context for drawing graphics - it doesn't maintain any image of what's been drawn. An Image is what contains imagery and graphics - a Graphics is what's used to draw this.
Therefore you're probably after creating an Image, passing that your your panel and drawing that in the paintComponent method.
Hope this helps a bit.