Programming in Java CSCI 2220

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Programming in JavaCSCI 2220

• Model-View-Controller (MVC)
• Design Pattern

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MVC Design Pattern

• Many typical GUI applications consist of views
  of some particular application state or model
• The GUI also includes mechanisms to manipulate or
  control the models state
• This allows the application data to be completely
  independent of the GUI design and also allows for
  multiple GUI views to represent the same model
  data in multiple different ways

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Example Application

• Windows Explorer provides a view of the file
  system
• Multiple different views represent the same file
  system in different ways using the split panes
• The application provides mechanisms to manipulate
  the file system. These mechanisms are
  representative of the controller in the MVC
  pattern

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MVC Structure

• Model
• Represents application state
• Exposes operations that can be performed on the
  model to the controller
• Notifies all registered views when changes to
  the model are made

State Change Requests
State Change Notifications

• Controller
• Provides an interface between the model and the
  view to facilitate user modifications
• Responds to user actions by notifying model of
  desired changes

• View
• Displays the model
• Responds to notifications from the model by
  updating the display

Often Combined as GUI elements
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MVC Pattern in Java

• Java provides a built in framework to facilitate
  the use of the MVC design pattern
• Your model must extend the Observable class
• Your views should implement the Observer
  interface
• One method public void update(Observable o,
  Object arg)
• Called by Observable objects for which the
  Observer is registered with
• The Observable class contains methods to
  facilitate adding Observers (views) to the model
  and also mechanisms to automatically notify all
  Observers that have been added when the model has
  changed

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Notes

• The Observer/Observable framework combines the
  view and the controller of the MVC pattern into
  one class (the Observer class)
• The Swing framework uses a similar modified MVC
  design structure (not Observer/Observable but
  most Swing components have an accessible model
  which is independent of the GUI component
  visualization implementation)
• For example JSlider is a GUI component that
  represents a user modifiable slider. The
  BoundedRangeModel class is its corresponding
  view class and each JSlider has a corresponding
  and user-definable BoundedRangeModel associated
  with it

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Homework

• Homework 6 due tonight at 1155 PM
• Final Project will be posted online soon
• Due May 4