Не могу понять, как работать с графикой

import java.awt.*;
import javax.swing.*;
 
public class Main {
  public static void main (String[] args)
  {
    MyFrame frame = new MyFrame ();
    frame.setDefaultCloseOperation (JFrame.EXIT_ON_CLOSE);
    frame.setVisible (true);
  }
}
 
class MyFrame extends JFrame
{
  public MyFrame()
  {
    this.setBounds (0, 0, 200, 200);
    
    MyPanel panel = new MyPanel();
    this.add (panel);
  }
}
 
class MyPanel extends JPanel
{
  public void paintComponent (Graphics g)
  {
    super.paintComponent (g);   
    g.drawLine (10, 10, 180, 180);  
  }
}

import javax.swing.*;
import javax.swing.border.Border;
import java.awt.*;
import java.awt.event.ComponentAdapter;
import java.awt.event.ComponentEvent;
import java.awt.image.BufferedImage;
 
public class Main {
  public static void main (String[] args)
  {
    JFrame frame = new JFrame ();
    frame.setBounds (0, 0, 200, 200);
    frame.setDefaultCloseOperation (JFrame.EXIT_ON_CLOSE);
    frame.setVisible (true);
  
//    MyPanel panel = new MyPanel();
//    frame.add (panel);
    
    JPanel panel = new JPanel();
    panel.setBackground(Color.green);
    frame.add (panel);
 
    JCanvas canvas = new JCanvas (200, 200);
    panel.add (canvas, BorderLayout.CENTER);
    Graphics2D g = canvas.createCanvasGraphics();
    g.drawLine (10, 10, 180, 180);
    canvas.repaint();
  }
}

public class Main {
  public static void main (String[] args)
  {
    JFrame frame = new JFrame ();
    frame.setBounds (0, 0, 200, 200);
    frame.setDefaultCloseOperation (JFrame.EXIT_ON_CLOSE);
    frame.setVisible (true);
  
    JPanel panel = new JPanel();
    panel.setLayout(new BorderLayout());
    panel.setBackground(Color.green);
    frame.add (panel);
 
    JCanvas canvas = new JCanvas (200, 200);
    panel.add (canvas, BorderLayout.CENTER);
    Graphics2D g = canvas.createCanvasGraphics();
    g.drawLine (0, 0, 180, 180);
    canvas.repaint();
  }
}

public class Main {
  public static void main (String[] args)
  {
    JFrame frame = new JFrame ();
    frame.setBounds (0, 0, 200, 200);
    frame.setDefaultCloseOperation (JFrame.EXIT_ON_CLOSE);
    frame.setVisible (true);
  
    JPanel panel = new JPanel();
    panel.setLayout(new BorderLayout());
    panel.setBackground(Color.green);
    frame.add (panel);
    frame.validate();
 
    JCanvas canvas = new JCanvas (200, 200);
    panel.add (canvas, BorderLayout.CENTER);
    panel.validate();
    Graphics2D g = canvas.createCanvasGraphics();
    g.drawLine (0, 0, 180, 180);
    canvas.repaint();
  }
}

import javax.swing.*;
import java.awt.*;
 
public class Main {
  public static void main (String[] args)
  {
    JFrame frame = new JFrame ();
    frame.setBounds (0, 0, 400, 300);
    frame.setDefaultCloseOperation (JFrame.EXIT_ON_CLOSE);
    frame.setVisible (true);
  
    JPanel panel = new JPanel();
    panel.setLayout(new BorderLayout());
    frame.add (panel);
 
    JCanvas canvas = new JCanvas (320, 200);
    panel.add (canvas, BorderLayout.CENTER);
    panel.validate();
 
    Graphics2D g = canvas.createCanvasGraphics();
    g.setColor (Color.yellow);
    g.fillRect(0, 0, 320, 200);
 
    g.setColor (Color.black);
    g.drawLine (10, 10, 310, 190);
    canvas.repaint();
 
    try
    {
      Thread.sleep (1000);
    } catch (InterruptedException e)
    {
      e.printStackTrace();
    }
    
    g.setColor (Color.black);
    g.drawLine (310, 10, 10, 190);
    canvas.repaint();
  }
}