Held: Wednesday, 8 December 2004
Summary:
Today we conclude our discussion of Design Patterns by quickly visiting and
relating the behavioral patterns.
Related Pages:
Assignments
Notes:
- Are there questions on the final examination?
- Are there questions on the final project?
- I have distributed participation grades. Let me know if you have questions or concerns.
Overview:
- Introduction
- Summary of patterns
- Relating patterns
- Questions
- Behavioral patterns take an object-oriented approach to the behavior of your program:
- How do we arrange objects to simplify algorithms?
- How do we arrange objects to improve method calls (message sends)?
- ...
- At times, the behavioral patterns seem (to me) to be attempting to simulate features from other languages.
- Command, Strategy, Template Method simulate key aspects of functional programming.
- Chain of Responsibility simulates handling of exceptions in a different way.
- Iterators come from an interesting imperative language.
- ...
- Some patterns discuss sending messages to multiple objects
- Chain of Responsibility - Provide a sequence of objects to handle each request
- Observer - Indicate that you want messages from an object
- Mediator - Mediate message passing between related objects
- Some patterns simulate functional programming
- Command - Encapsulate a function in an object
- Strategy - Encapsulate a function in an interface
- Template Method - Encapsulate the skeleton of a function in an interface; Parameterize through subclassing
- Visitor - Map
- Some patterns provide mechanisms for visiting complex structures
- Interpreter - Build structures and visit them
- Iterator - Provide a separate object to visit structures
- Visitor - Require clients to provide an object and move it through the structure
- Some patterns have to do with state
- Memento - Package and unpackage state
- State - Switch state by changing a contained class
- Observer - Notify objects about state changes
;
Check with Bobby