G6DICP - Lecture 17

1
G6DICP - Lecture 17

• GUI (Graphical User Interface) Programming

2
Java GUI Class Libraries

• AWT Abstract Windows Toolkit
• Small and relatively simple GUI library
• Bundled with JDK 1.0
• Major revisions in JDK 1.1 (not compatible with
  1.0)
• No fundamental changes since JDK 1.2 (Java 2)
• Swing Java Foundation Classes
• Large GUI library essentially a superset of AWT
• The Swing Set
• Compatible with JDK 1.1 (not included)
• Bundled with Java 2
• Swing and AWT are similar in principle, but Swing
  is very much larger both in terms of number of
  classes and methods.

3
Major GUI concepts

• Windows
• Containers
• Components
• Events

4
The Java Frame class

• java.awt.Frame
• Frame objects represent windows
• Graphical programs (almost) always have at least
  one Frame
• Rarely used directly usually subclassed
• Invoking the show() method causes window to be
  displayed
• The constructor of a Frame is usually where
  initialisation code is placed (and often most of
  the layout/UI of a graphical program)

5
The Paint Method

• java.awt.Frame.paint(Graphic g)
• Executed automatically whenever the screen is
  redrawn
• Overriden to contain code that writes to the
  screen
• Be careful
• Avoid accidental recursion
• The paint method should never be invoked directly
• Since paint is executed every time the screen is
  redrawn do not do anything time consuming in
  it, e.g.
• File i/o
• Large loops or recursion
• Complex calculations

6
The Graphic Class

• java.awt.Graphic
• Abstract class containing various drawing methods
• Never instantiated in code
• Instantiated by the VM, and an instance passed
  into the paint() method
• Methods of this instance are used to write onto
  the screen