Review

1
CSC 335 Object-Oriented Programming and Design
Review Strategy Design Pattern MVC
2
Pattern Strategy

• Name Strategy (a.k.a Policy)
• Problem You want to encapsulate a family of
  algorithms and make them interchangeable.
  Strategy lets the the algorithm vary
  independently from the clients that use it (GoF)
• Solution Create an abstract strategy class (or
  interface) and extend (or implement) it in
  numerous ways. Each subclass defines the same
  method names in different ways

3
Pattern Strategy

• Consequences
• Allows families of algorithms. Known uses
• Layout managers in Java
• Different Poker Strategies in 335 Projects
• Different Packman chase strategies 335 Fall 2001
• TextField validators in dBase and Borland OWL
• Will use different algorithms to verify if the
  user input is a valid integer, double, string,
  date, yes/no.
• Eliminates conditional statements
• Don't need to keep asking, if this is supposed to
  be an int do this, else if it is a string do that

4
Java Example of Strategy

• this.setLayout( new FlowLayout( ) )
• this.setLayout( new GridLayout( ) )
• In Java, a container contains a layout manager
• There is a default perhaps set in the
  constructor
• You can change a container's layout manager with
  a setLayout message
• Could use same approach in Ghosts
• Ghosts have common methods but could change an
  instance variable at runtime with
• setStrategy( new RandomStategy( ) )

5
interface LayoutManager

• Java has a java.awt.LayoutManager interface
• Known Implementing Classes
• GridLayout, FlowLayout, ScrollPaneLayout
• Each class implements the following methods
• addLayoutComponent(String name, Component comp)
  
• layoutContainer(Container parent)
• minimumLayoutSize(Container parent)
• preferredLayoutSize(Container parent)
• removeLayoutComponent(Component comp)

6
General form of Strategy in UML (abstract)
ltltinterfacegtgt Strategy AlgorithmInterface
Context strategy Strategy ContextInterface
implements
ConcreteClassA AlgorithmInterface
ConcreteClassB AlgorithmInterface
ConcreteClassC AlgorithmInterface
7
Specific UML Diagram of LayoutManager
ltltinterfacegtgt LayoutManager addLayoutComponent() l
ayoutContainer() minimumLayoutSize()
JPanel panel Panel size Dimension layoutBoss
LayoutManager setLayout(lm LayoutManager) setPref
erredSize(diDimension)
implements
GridLayout addLayoutComponent() layoutContainer()
minimumLayoutSize()
FlowLayout addLayoutComponent() layoutContainer()
minimumLayoutSize()
ScrollPaneLayout addLayoutComponent() layoutContai
ner() minimumLayoutSize()
8
Change the strategy at runtime

• Demonstrate LayoutControllerFrame.java
• Source code online and attached
• private class FlowListener implements
  ActionListener
• // There is another ActionListener for
  GridLayout
• public void actionPerformed( ActionEvent evt )
• // Change the layout strategy of the JPanel
• // and tell it to lay itself out
• centerPanel.setLayout( new FlowLayout( ) )
• centerPanel.validate( )

9
Another Example
10
Another Example
11
Another Example

• OozinOz has strategies to decide which Fireworks
  to recommend to customers
• See Pages 237..247

12
Observer Design Pattern

• Observer Define a 1 to many relationship so when
  one object changes state, all dependents are
  notified and they update the view themselves.
• You will be able to switch views at runtime or to
  show 2 or more views at the same time
• Java supports this with Observer/Observable
• BattleBoat and Poker must use this pattern
• MUD could

13
OOP and UI

• Decoupled UIs are good
• One model may have several user interfaces
• Web, phone, PDA, GUI on a desktop
• Each UI will hook into the same model
• But allow IO in different ways
• Desired change UI without changing the model
• Desired change the model without changing the UI
• Do not imbed the UI code inside the model
• Keep the two separate Model-View Separation

14
MVC

• Model-View-Controller (MVC) you have used this in
  you event-driven programs with a GUI and in your
  final project
• Model Represents system with the business logic
• View Displays the model
• Controllers Handle user interaction and sends
  correct messages to the model and/or view

15
Model

• The Model's responsibilities
• Provide access to the state of the system
• Provide access to the system's functionality
• Can notify the view(s) that its state has changed

16
Controller

• The controller's responsibilities
• Accept user input
• Button clicks, key presses, mouse movements,
  slider bar changes
• Send messages to the model, which may in turn
  notify it observers
• Send appropriate messages to the view
• In Java, listeners are controllers

17
View

• The view's responsibilities
• Display the state of the model to the user
• At some point, the model (a.k.a. the observable)
  must registers the views (a.k.a. observers) so
  the model can notify the observers that its state
  has changed

18
from http//www.enode.com/x/markup/tutorial/mvc.ht
ml)
19
State Pattern