Programming Languages
2nd edition
Tucker and Noonan
Chapter 16
Event-Driven Programming
Of all men’s miseries the bitterest is this, to know so much and
to have control over nothing.
Herodotus (484-432 BC)
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Contents
16.1
16.2
16.3
16.4
Event-Driven Control
Event Handling
Three Examples
Other Applications
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A conventional model of computation has the program
prescribe the exact order of input.
Programs terminate once the input is exhausted.
Event-driven programs do not control the sequence in
which input events occur.
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Examples
GUI applications: Model-View-Controller design
Embedded applications:
cell phones
car engines
airplanes
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16.1 Event-Driven Control
Computation as interaction [Stein]
Computation is a community of persistent entities
coupled together by their ongoing interactive
behavior ... Beginning and end, when present, are
special cases that can often be ignored.
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Imperative and Event-Driven Paradigms Contrasted
Figure 16.1
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Input to an event-driven program comes from
autonomous event sources. Eg: human, robot
sensors, engine sensors.
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Properties
1. An event-driven program has no perceived
stopping point.
2. The traditional read-eval-print loop does not
explicitly appear.
3. An application processes an input and exits.
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Model-View-Controller (MVC)
• Model: the object being implemented. Ex: game,
calculator.
• Controller: input mechanisms. Ex: buttons, menus,
combo boxes.
• View: output.
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Ex: Tic-Tac-Toe Model
• Whose turn is it?
• State of the board.
• Has someone won?
• Are there no empty squares?
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Events in Java
• Subclasses of AWTEvent
• Event sources in Swing are subclasses of
JComponent
• Program must listen for events
• Ex: for a JButton b
– b.addActionListener(listener)
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Java Class AWTEvent and Its Subclasses*
Figure 16.2
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Java EventListener Class Interface and Its Subclasses*
Figure 16.4
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Widget
Listener
Interface
JButton
ActionListener
actionPerformed
JComboBox ActionListener
actionPerformed
JLabel
JTextArea
ActionListener
actionPerformed
JTextField
ActionListener
actionPerformed
MouseListener
...
MouseMotionListener
...
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Java GUI Application
A GUI application is a program that runs in its own
window and communicates with users using
buttons, menus, mouse clicks, etc.
A GUI application often has a paint method, which is
invoked whenever the application needs to repaint
itself.
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16.3.2 Designing a Java Applet
• Can convert previous application
• An applet runs inside a web browser
• Differences
– Extend JApplet
– Lacks a main method
– Method init replaces constructor
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Tic-Tac-Toe
• State of the board
• Whose turn: X or O
• Whether game is over
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private int player = -1; // Current player: EX, or OH
private int[ ] board = new int[9];
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Elements of a Typical ATM Machine
Transaction User Interface
Figure 16.25
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Overall Design of a Home Security System
Figure 16.26
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