Special Effects and Game Development
in Java(TM) - How to draw on the applet screen with the paint()
method (the Graphics class and the fillRect() method)
by Anibal Wainstein
2.1.3 How to draw on the
applet screen with the paint() method (the Graphics class
and the fillRect() method)
I said in section 2.0.2 that there
was the init() method that was the first thing executed in
a Java applet. The method that is called directly after init()
in an applet is the paint() method:
public void paint(Graphics g)
{ }
With the paint() method you have full control over the applet
screen thanks to the Graphics object that is included and that
is connected to the screen. In the Graphics class there are
methods to draw lines, circles, rectangles, texts, Images and
more. You should always update a graphics applet by initializing
the screen with a certain background color. This we can do
with the fillRect() method that will draw a filled rectangle.
First we must specify a color that the applet's "pen"
will work with.
Let us say that we want blue color in our applet and that the
applet size must be 200x100 pixels:
import java.applet.*; import java.awt.*;
public class initbackground extends Applet {
public void paint(Graphics g)
{
Color backgroundcolor = new Color(0,0,255);
//setColor() in the Graphics class
//sets the color of the pen
g.setColor(backgroundcolor);
//fillRect() fills a rectangular area with the
//selected color. The method requires a horizontal
//and vertical position (x and y position)
g.fillRect(0,0,200,100);
}
}
Note that all the communication with the applet screen is
done with the graphics object "g". In the example
above we have first set the color on the pen that the Graphics
object will use to draw on the screen, in this case blue.
Next step is to draw a rectangle that covers the entire screen
with the color we have chosen. We wanted an applet with the
dimensions 200x100, therefore we need to draw a rectangle
that is drawn to the left and above (position 0,0) and has
the same dimensions as the applet.
NOTE that if you increase the vertical position y
then the rectangle is moved downwards. An increase of the
horizontal position x moves the rectangle to the right.
The fillRect() method's functionality.
Now make a file of the code text above and your own HTML
file where CODE="initbackground.class" and where
WIDTH=200 and HEIGHT=100.
You can also click here
to see the applet.
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