The Java Abstract Window Toolkit Package java'awt

1
The Java Abstract Window Toolkit Package -
java.awt

• It contains classes to work with
• graphics, mouse and keyboard
• graphics components (Java GUI)
• events
• images
• data transfer
• We will look at some of the methods and constants
  in the Graphics class

2
Representing Color

• A black and white picture can be stored using one
  bit per pixel (0 white and 1 black)
• A colored picture requires more information
• Every color can be represented as a mixture of
  the three primary colors Red, Green, and Blue
• In Java, each color is represented by is a triple
  of whole numbers (r, g, b) defining the amount of
  red, green and blue colour called an RGB value
• Each r, g and b value is a number between 0 and
  256 thus enabling the Java programmer to choose
  from approximately 16 million! colours

3
The Color Class

• Every drawing surface has a background color
• Every graphics context has a current foreground
  color
• Both can be set explicitly

4
Color Control

• Class Color - methods and constants for
  manipulating colours
• Colour constants white, black, blue, etc.
• Defining new colour Color ( r, g, b )
• Get the colour of a particular pixel getRed( ),
  getGreen( ), getBlue( ), getColor( )
• Set the colour to draw with setColor ( Color c )
• For more methods check the Java API documentation

5
Color Constants
6
The Color Class

• A color is defined in a Java program using an
  object created from the Color class
• You can use the colour constants by referring to
  the Color class and using the dot operator

Color.black Color.blue Color.cyan Color.orange Co
lor.white Color.yellow
7
Using Colors - Examples

• Graphics g
• g.setColor( Color.red )
• g.setColor( new Color( 0, 64, 255 ))
• Color color1 Color.green
• g.setColor( color1 )

8
Font Control

• Class Font - methods and constants to change the
  font name, font size and font style
• Constants
• font names - Serif, SansSerif, Dialog,
  DialogInput, Monospaced
• font style - Font.BOLD, Font.ITALIC, Font.PLAIN
• Method to change the Font
• Font( fontName, fontStyle, fontSize )

9
Font Control - Examples

• Font font1 new Font ("SansSerif", Font.ITALIC,
  5)
• Font font2 new Font (Serif", Font.ITALIC
  Font.BOLD, 10)
• Font font1 new Font (Monospaced", Font.PLAIN,
  24)
• Font font1 new Font (Dialog", Font.ITALIC,
  10)

10
Co-ordinate System

• When drawing on the screen we use a co-ordinate
  system
• In the Applet screen even strings are drawn!
• Co-ordinate System
• (0, 0) upper left corner of an applet or window

11
Co-ordinate System - Example

• import java.applet.Applet
• import java.awt.Graphics
• public class StarTriangle extends Applet
• public void paint( Graphics g )
• g.drawString( "", 70, 70 )
• g.drawString( "", 70, 80 )
• g.drawString( "", 70, 90 )

12
Co-ordinate System - Example
X axis
(0, 0)
70
70
(70, 70)
80
(70, 80)
90
(70, 90)
Y axis
13
Drawing Shapes

• In the Graphics class you have methods to draw
• Lines
• Rectangles
• Polygons
• Ovals (cyrcles)
• Arcs
• A shape can be filled with colour or unfilled,
  depending on the method invoked
• The method parameters specify coordinates and
  sizes

14
Drawing Shapes (2)

• Drawing a shape
• drawLine( x1, y1, x2, y2 )
• drawRect( x, y, width, height )
• drawRoundRec( x, y, width, height,
  arcWidth,arcHeight )
• drawOval( x, y, width, height )
• Drawing a solid shape filled with particular
  colour
• fillRect( x, y, width, height )
• fillRoundRec( x, y, width, height,
  arcWidth, arcHeight )
• fillOval( x, y, width, height )

15
Drawing Shapes (2)

• Shapes with curves, like an oval, are usually
  drawn by specifying the shapes bounding
  rectangle
• An arc can be thought of as a section of an oval

16
Drawing a Line
17
Drawing a Rectangle
50
20
drawRect (50, 20, 100, 40)
18
Drawing an Oval
150
20
bounding rectangle
drawOval (150, 20, 40, 60)