What is the top level component passed to the paint() call?

Question

Reviewing some tutorials related to Java and graphics and constantly seeing the following :

public void paint (Graphics g) 
{
     Graphics2D g2;
     g2 = (Graphics2D) g;
       :
       :
}

Both Graphics and Graphics2D are abstract classes. Plus, Graphics2D is a subclass of Graphics. As a result, the cast from Graphics to Graphics2D (g2 = (Graphics2D) g;) shouldn't work, right?

public class Object1 {
    int obj1Var1;
    public void obj1_Method1()
    {
        System.out.println("Inside Object1:Method1");
    }
}

public class Object2 extends Object1{
    int obj2var1;
    public void obj2_Method1()
    {
        System.out.println("Inside Object2:Method1");
    }
}

Using the above, which is sort of a parallel with the Graphics / Graphics2D scenario shows that it fails using the following.

Object1 obj = new Object1();
Object2 obj2 = (Object2)obj;   <----This fails as expected. 

Since the cast from Graphics to Graphics2D works (especially since they are abstract objects) then the original object in memory must already be a Graphics2D and defines the abstract methods. So, which is the actual underlying object in memory that is being referenced by the Graphics object being passed to the paint() call?

Answer 1

In Oracle JDK, the class is called sun.java2d.SunGraphics2D. You can run this program to see what it is in your version of Java:

import java.awt.Graphics;
import javax.swing.JFrame;

public class SwingTest {
    private static class Frame extends JFrame {
        @Override
        public void paint(Graphics g) {
            super.paint(g);
            System.out.println(g.getClass().getName());
        }
    }

    public static void main(String[] args) {
        Frame frame = new Frame();
        frame.setVisible(true);
    }
}