Java Tutorial for Beginners - 44 - GUI - Graphics and the Paint method

In this tutorial we will take a first look at graphics.

[samraspin]

This is by far the best tutorial on this topic. Helped me out a lot. Cheers

[manicho]

One of the few who got all the way here! :D

[hubertuswine]

Awesome tutorials, helped a lot while reviewing stuff for a programming exam!

[punated]

I have two questions here...
1) why can't paint right onto JFrame(Why the Panel)? I tried and have to change the 
paintComponent method to another name (paint(Graphics g) to get it to put the rectangle in there, but it does....

2) frame.add(this):  is the reason for this is that since we extend JPanel, our graphic is being created on the panel, and frame.add(this) adds "this panel" or is that logic off?

[nailmirror]

Is there a way to edit the paintComponent() method of your JPanel without extending off of it?

[Senshiii]

I like creating graphics in JFrame as compared to an Applet and my question is in Applet I can use repaint() but in this way(i.e. when using paintComponent())
how do I use repaint() or a
some function like it??

[EJMedia]

Source:
import java.awt.*;
import javax.swing.*;

// 1. Added components to our JFRAME
// 2. We can also add graphics but NOT to JFRAME - need to use JPANEL

public class Rectangle extends JPanel {
JFrame frame;
    
    public void fireUpScreen () { 
        
    frame = new JFrame ();
    frame.setVisible(true);
    frame.setSize (600, 600);
   
    frame.add(this);
    }
    
public void paintComponent (Graphics g) {
    
// paintComponent is the method used to paint - think of JPanel as our canvas
g.setColor(Color.BLUE);
g.fillRect(0, 0, 200, 100);
    
}
    public static void main(String[] args) {
        Rectangle go = new Rectangle ();
        go.fireUpScreen();
    }

}

[sraj]

I'm very confused about 2 things here:
1. Is this method paintComponent inherited from Jpanel's super classes, or is it a method that you have custom written (Your oen function)?
2. When Rectangle class is instantiated as go(), I don't see how this painComponent method gets invokes anywhere from the main method. How does the control even reach here? I was thinking that the only way this can be invoked is by go.paintComponent(Graphics g)?

[chrisszeremet]

Why don't you call paintComponent method?