Graphics

1
Graphics

• Robert Salkin
• CSI 205 OOP using Java
• Summer 2005, 6W1

2
Quick Review

• Random is the class used to generate
  pseudo-random numbers.
• Random objects should be seeded with a different
  number each time the program is run in order to
  get a greater level of randomness.
• The nextInt() method should be passed a maximum
  integer one greater than the actual maximum
  number that should be returned.

3
Lightweight vs. Heavyweight

• Lightweight GUI components dont have direct
  interaction with the system.
• They should appear the same anywhere.
• Swing was written to add lightweight GUI
  components.
• GUI components starting with J are mostly
  lightweight, however some might have underlying
  heavyweight interaction.
• Heavyweight GUI components have some direct
  interaction with the system.
• These components can have problems on some
  systems.
• AWT components are heavyweight.

4
Component

• The class Component is a direct or indirect
  superclass of most GUI components.
• A GUI component is a discrete GUI object, like an
  instantiation of JButton, JPanel, or JTextField.

5
Container

• The class Container is a superclass of GUI
  components that can hold other GUI components.
• Example classes that are normally used as
  containers are JPanel and JFrame.
• A Container object is a Component object, so
  anywhere a Component object may be used, a
  Container object may be used.

6
X Y

• Shapes are drawn using X and Y coordinates.
• X goes from 0 to greater than 0 from left to
  right.
• Y goes from 0 to greater than 0 from top to
  bottom (not bottom to top as in mathematics).

7
Graphics

• A Graphics object manages Javas ability to draw
  on the screen in a graphics context.
• Graphics is an abstract class, therefore only
  subclasses may be instantiated.

8
Color

• A Color object is required when a non-default
  color is desired.
• Color objects are set to a specific color by
  passing their Red, Green, and Blue (or RGB)
  components to the constructor.
• Methods are available to set the color directly.
• Alternatively, public static final Color objects
  are available for use, like Color.RED or
  Color.LIGHT_GRAY.

9
Paint and Repaint

• GUI components need to be drawn on the screen
  using a Graphics object referencing the
  appropriate graphics context.
• The paintComponent method is overridden to draw
  objects on the screen.
• public void paintComponent(Graphics g)
• Always call super.paintComponent(g)
• The repaint() method is calle when the programmer
  wants objects to be updated on the screen.

10
Graphics Methods

• setColor(Color c)
• Sets the current color.
• fillRect(int x, int y, int width, int height)
• Draws a filled in rectangle.
• drawString(String str, int x, int y)
• Draws a line of text.
• setBackground(Color c)
• Sets the background color of a JComponent.
• NOT part of Graphics, so use the JComponent
  reference.
• Many others

11
Anonymous Inner Class

• An anonymous inner class is a class declared
  inside of another class without a name and
  usually appears in a method call relating to a
  listener.

12
Adapter Class

• An adapter class implements an interface using
  empty methods.
• An adapter is useful when only certain methods of
  a class are important to an implementation.

13
MouseListener

• A MouseListener listens for MouseEvents similar
  to the way an ActionListener listens for
  ActionEvents on GUI components.
• The MouseAdapter class is an adapter that is
  useful to use when only one or a few mouse events
  are relevant to the program.
• When motion of the mouse matters,
  MouseMotionListener and MouseMotionAdapter may be
  used.

14
MouseEvent Methods

• getPoint()
• Gets a Point representing the X and Y position of
  the mouse.
• getX()
• Gets the X coordinate of the position of the
  mouse.
• getY()
• Gets the Y coordinate of the position of the
  mouse.

15
Problem

• How do all of these classes work together?
• Example