Design Again

Objectives

1. Briefly discuss design methods

Notes

• We have been using a design method called Top Down Design
  • Look at the problem and break it up into big steps.
  • Then break the big steps down
  • Repeat this until you get down to steps that are easy to implement.
• This method is also called functional decomposition.
  • Because you think about how you are going to "do" the problem in terms of steps, which you implement as functions or methods.
• In general we want to build functions that are "cohesive"
  • A cohesive function is a function that does one thing.
  • You should be able to find a good name for a cohesive function.
• This leads to a type of programming called procedural programming
  • This is NOT functional programming, which is a very different beast.
• We learned in the 60's that top down design might not be the best way to go.
  • It does not scale well.
  • And when a project is large, involving many people, it tends to fall apart.
• An alternative is object oriented design.
  • In this case, we look at the pieces or objects that make up our problem.
  • These might be real or just logical
    • If you were simulating Monopoly, you would have property objects, a board object, possibly money objects, player object ...
    • If you were writing a banking application, you would have a customer object, different account type objects (loan, savings) ...
  • You then combine these objects to form larger systems to eventually solve the problem
• This is sometimes called bottom up design, as you look a the little pieces first.
• This type of design focuses on data and what you do to the data rather than on steps to solving a problem.
• Both are valid, and both are used.
• Java is specifically an object-oriented language and you will be learning OO design.