Creating Graphics in Java

1
Creating Graphics in Java

• CSE301
• University of Sunderland
• Harry R Erwin, PhD

2
Resources

• Flanagan, David (2000). Java Foundation Classes
  in a Nutshell, OReilly.
• Darwin, Ian F. (2004). Java Cookbook, OReilly.
• Flanagan, David (2004). Java Examples in a
  Nutshell, OReilly.

3
Java GUI Frameworks

• Abstract Window Toolkit (java.awt)
• The original set of windowing components designed
  for Java. These were implemented as separate
  processes using the GUI features of the
  underlying operating system.
• Swing (or Java Foundation Classesjavax.swing)
• A second generation set of light-weight
  windowing components introduced in Java 1.2.
  These were implemented as Java threads and so
  avoided the overhead of process context switches
  and enforced a common look and feel.
• SWT (part of Eclipse)
• Discussed at http//java.sun.com/docs/books/tutor
  ial/uiswing/index.html

4
Goals

• The goal of these two lectures is to provide the
  student an understanding of graphics in Java.
• GUI1 explores the Java 2D API, the basic graphics
  primitives.
• GUI2 explores image processing, image I/O, and
  animation.

5
Review of AWT

• The foundation of GUI in Java
• Implemented in separate processes
• Rudimentary
• Supported by most web browsers, so that most
  applets should use AWT instead of Swing.

6
AWT Graphics Features

• Basic facilities for creating a graphical user
  interface.
• Drawing graphics
• java.awt.Graphics
• java.awt.Color
• java.awt.Font
• Java 2D API (added in Java 1.2)
• java.awt.Graphics2D

7
Using AWT

• Import
• java.awt.
• java.awt.event.
• Everything inherits from java.awt.Component,
  including graphics.
• The AWT GUI is organized by containers,
  inheriting from java.awt.Container (which
  inherits from Component).
• The arrangement of controls is managed by various
  layout managers.
• Notification of changes is handled by events and
  event listeners that run in a GUI thread.

8
Graphics Before Java 1.2

• Demonstrated in GraphicsSampler.java from Java
  Examples in a Nutshell (library).
• init() is called to initialise color resources.
• paint() is called every time the object needs to
  be redrawn, for example when the applet is
  covered by another window and the window moves or
  disappears.

9
The Graphics Object

• Used for all graphics operations prior to 1.2
• Represents a drawing surface. Can be used to draw
  on a Component, Image, or printer.
• Keeps track of the current state.
• Provides attributes and methods for drawing.

10
java.awt.Graphics

• An interface.
• Cannot be created directly. You must
• use getGraphics() on a Component
• use getGraphics() on an image or PrintJob
• copy from an existing Graphics object using
  create().
• When no longer needed, call dispose() on it to
  free up the system resources it uses.

11
Graphics Attributes

• Color, the current Color object
• Font, the current Font object
• Clipping region, the Rectangle to be painted
• Origin, a point
• Paint mode, a boolean
• Background color, a Color

12
Graphics Operations

• drawLine() (1 pixel)
• drawPolyLine() (polygon)
• drawArc()
• drawOval()
• drawPolygon()
• drawRect()
• drawRoundRect()
• draw3DRect()

• fillArc()
• fillOval()
• fillPolygon() (polygon)
• fillRect()
• fillRoundRect()
• fill3DRect()
• drawBytes() (byte)
• drawChars() (char)

13
More Graphics Operations

• drawString()
• drawImage()
• various versions, requiring an ImageObserver
  object
• clearRect()
• various setters and getters
• copyArea()

• clipRect()
• translate()
• hitClip()
• translate()

14
java.awt.Font

• Represents a font. The constructor is passed a
  name, a style (PLAIN, BOLD, ITALIC, BOLDITALIC),
  and a font size.
• Names include
• serif
• sansserif
• monospaced
• Dialog
• DialogInput
• Symbol

15
java.awt.Color

• Represents colors.
• Can represent a color coded in RGB space defined
  from integers or floating point numbers.
• Has a static method that allows you to create
  colors in the HSB color space.
• Provides some standard colors as constants, such
  as Color.black or Color.white.
• java.awt.SystemColor is a subclass with constants
  for various colors used on the system desktop.

16
java.awt.Rectangle

• Defines a rectangle using the x and y coordinates
  of the upper left corner and the width and
  height. These four values are public and can be
  manipulated directly.
• Used to define rectangular regions, usually in an
  image being manipulated.
• Can be used for other purposes.

17
java.awt.Point

• A concrete subclass of java.awt.geom.Point2D
• A Point is defined as two integers, x and y.
  These are public fields and can be manipulated
  directly.
• equals() is overridden so two points are equal if
  they have the same x and y values.
• hashCode() doesnt appear to be overridden, so
  dont use a Point as an index in a HashMap with
  the expectation that it will be a value class.

18
This Weeks Exercise

• Access http//www.oreilly.com/catalog/jenut3
• Download the sample code and create an Eclipse
  project for GraphicsSampler.java (an Applet)
• Run the Applet in the debugger so you can observe
  how it works.