Agenda For Feb 23

1
Agenda For Feb 23
1. PowerPoint Presentation on Colors and
Polygons
2. Finish up Unit 3 Exercises on page 20

• 3. Create a Happy Face Java Applet (due next
  class). Criteria
• Use lines for the hair (at least 5 lines)
• Use ovals for the eyes (fill the ovals with a
  color you create from scratch).
• The nose must be a polygon.
• Use at least one arc for the mouth.
• Your Happy Face must use at least 3 different
  colors.

4. Unit 4 Exercises on page 33. Question 2
2
Using Colors

• There are two ways you can set the current
  drawing color. You can use pre-defined Java
  colors or you can define your own color from
  scratch. This is how you can set the current
  drawing using the pre-defined Java color red.
• screen.setColor (Color.red)

You can replace the word red with any other Java
pre-defined color.
3
Creating Your Own Color
The following is a list of the available
pre-defined Java colors (found on page 27) red,
blue, cyan, gray, darkGray, lightGray, green,
magenta, orange, pink, white, yellow

• You can also set the current drawing color
  using a color you created from scratch. This is
  how you can create and set your own drawing color
  from scratch.

Color myColor new Color (255, 0, 0)
screen.setColor (myColor)
4
RGB Colors

• These three parameters can be any integer
  between and including 0 to 255. The 255s in the
  images above mean I want a particular color to be
  turned on full blast and the zeros mean I dont
  want to add any of that particular color. What
  color would the RGB combination (255, 0, 255)
  make?

5
Drawing Polygons

• So far weve seen that Java provides us with
  pre-defined colors (red, green, etc) and shapes
  (circles, rectangles, etc). However, if the need
  arises we are able to make up our own color up
  from scratch. What happens when we need to create
  a shape that isnt like any of the ones Java
  provides? You guessed it! We create our own
  shape from scratch. It takes more work because we
  have to define the shape ourselves, but thats
  the price you pay for being able to customizing
  your program so that it may better suite the
  needs of your users.

6
Drawing Your Own Shapes

• Drawing your own shape requires four steps.

1. Declare a polygon variable.
2. Initialize your polygon variable.
3. Define the vertices of your new polygon.
4. Draw your polygon.
1. In your variable section declare a Polygon
variable
public void init () Polygon mypoly
7
Initializing Your Polygon
2. In the init method, initialize your variable.
The textbook initializes this variable in the
paint method (page 29). This is not a good idea
because your applet program executes the paint
method many times and there is no point in
initializing the same variable over and over
again. Variables only need to be initialized
once. This is how you initialize the polygon
variable within the init method.
mypoly new Polygon()
8
Adding Points To Your Polygon

• 3. Use the addPoint method to define all the
  point of your polygon (do this inside your init
  method). NOTE The last point will
  automatically connect itself to the first point
  you defined. Your init method should now look
  like this

public void init() myPoly new Polygon() //
step 2 mypoly.addPoint (10, 10)
mypoly.addPoint (110, 10) mypoly.addPoint (60,
100)
9
Drawing Your Polygon
4. Now finally you can draw your polygon using
the method fillPolygon or drawPolygon.
public void paint (Graphics screen) screen.fill
Polygon (myPoly)
10
The Whole Program

• import java.awt.

import java.applet. public class HelloWorld
extends Applet  
Polygon myPoly
public void init() myPoly new Polygon()
mypoly.addPoint (10, 10)
mypoly.addPoint (110, 10)
mypoly.addPoint (60, 100)

public void paint(Graphics screen)
screen.fillPolygon (myPoly)

11
mypoly.addPoint (110, 10)
screen.fillPolygon (myPoly)
mypoly.addPoint (10, 10)
mypoly.addPoint (60, 100)
screen.drawPolygon (myPoly2)