Class Diagrams

• Class Diagram Tutorial

• The Pizza Problem

  Pizzas come in two types, round and square. Round Pizzas have 12 in diameters and cost $12.55 Square Pizzas are 15 inches on a side and cost $15.00 We are interested in knowing which Pizza is cheaper?

  A proposed architecture illustrated using a UML Class Diagram after identifying classes etc.

  Easier to understand than... Shape.java Circle.java Square.java Pizza.java

  Design patterns are

  1. Effective use of the OO Paradigm. Using the patterns results in flexible, malleable, maintainable code. It usually allows plug and play additions to existing code. It is like a good algorithms book is to procedural programming languages.
  2. It gives developers a vocabulary to talk about recurring class organizations. Now when you look at a class diagram, and parts are labelled with certain patterns, you can better understand the relationships between the classes.

  Composite Design Pattern

  
  
  
  • Represent linked lists, trees. x is composed of things like x
  • Can systematically add operations to structure
  • Removes 'end of list' checks. Everyone does what they are supposed to do.
  • Example

  Strategy

  
  
  • Separate an object and its behaviour. Allows for pluggable behaviours.
  • Example

  Observer-Observable