Event Driven Programming

1
Event Driven Programming

• Gary Greer

2
Event Driven Programming?

• basic programming uses sequence, selection, and
  repetition
• these methods are useful in producing programs
  that start, run and terminate
• modern programs, however, are expected to
  continually run and react to the user
• as it turns out, it is quite complex to write
  programs like this and so we turn to event driven
  programming

3
How Does it Work?

• the program starts running and waits for
  something to happen
• the programmer sets up a listener to listen for
  some event to happen
• when the event happens (say a button gets
  pressed) a group of instructions are executed
• usually then the program goes back to the waiting
  mode

4
Listeners

• there are a number of software objects that can
  listen
• buttons, menus, sliders, windows, timers, etc.
• you can also listen for events from physical
  devices
• mice, keyboards
• when the event occurs, the listener calls a
  section of code defined by the user

5
An Example

• //... Create components
• JButton faceButton new JButton("Change Face")
• //... Add Listeners
• faceButton.addActionListener(new FaceAction())
• /
• inner listener class that does the eye action
  
• /
• class FaceAction implements ActionListener
• public void actionPerformed(ActionEvent e)
  
• drawing.faceChange()