Lab3: Graphics and Painting

Most of the codes and activities source: Introduction to Programming Using Java, Sixth Edition

Some important reminders about painting

  • "Every component is responsible for drawing itself. If you want to use a standard component, you only have to add it to your applet or frame. You don't have to worry about painting it on the screen. That will happen automatically, since it already knows how to draw itself."
  • "Sometimes, however, you do want to draw on a component. You will have to do this whenever you want to display something that is not included among the standard, pre-defined component classes. When you want to do this, you have to define your own component class and provide a method in that class for drawing the component."

Activity

To make what is shown in demo, you could use the below structure of the code: (This is just an example, you could create your own) 
import java.awt.*;
import java.awt.event.*;
import java.awt.geom.*;

public class MoodClass extends JPanel implements MouseListener, ActionListener{
public MoodClass(){
// TODO: MoodClass Constructor
}
public void paintComponent(Graphics g) {
 super.paintComponent(g); //all the basic behaviours are taking care of
// TODO: Do all your painings on the screen here
}
public static void main(String[] args) {
// TODO: Make your JFrame here
// TODO: Make an object of your MoodClass which is a JPanel
// TODO: Make the JFrame to show your content 
	}//main
}
Hints:
  • What happens if the content of the components or your painings needs to be changed in the middle of the program? You should not call paintComponent() directly to make the change; this method is meant to be called only by the system. Instead, you have to inform the system that the component needs to be redrawn, and let the system do its job by calling paintComponent(). You do this by calling the component's repaint() method.
  • The paintComponent() method must be smart enough to correctly redraw all the paintings at any time. To make this possible, a program should store data in its instance variables about the state of the component. These variables should contain all the information necessary to redraw the drawings completely. The paintComponent() method should use the data in these variables to decide what to draw. When the program wants to change the content of the component, it should not simply draw the new content. It should change the values of the relevant variables and call repaint(). When the system calls paintComponent(), that method will use the new values of the variables and will draw the component with the desired modifications.
  • To know the size of your JPanel your could call: 
    (your JPanel object).getWidth();
(your JPanel object).getHeight();
  • If you want to use properties of Graphics2D, you could change your graphics to: 
     Graphics2D g2 = (Graphics2D) g;
  • There are different methods for drawing: 
    (Your Graphics2D object).drawString(...);
(Your Graphics2D object).fill(...);
(Your Graphics2D object).draw(...);
    For this activity, you need to draw the following shapes: Ellipse2D Arc2D Rectangle2D Example: making a filled ellipse: 
    g2.fill(new Ellipse2D.Double(x, y, width , height));