SWE202: GRASP Patterns in Software Construction

GRASP Patterns

• GRASP (General Responsibility Assignment Software Patterns) is an acronym created by Craig Larman to encompass nine object-oriented design principles related to creating responsibilities for classes.
• GRASP patterns are a learning aid to help with fundamental object design and apply design reasoning in a methodical, rational, explainable way.

Responsibilities

• A responsibility is a contract or obligation of a classifier.
• There are two types of responsibilities:
  • Doing responsibilities: include doing something itself, initiating action in other objects, and controlling and coordinating activities in other objects.
  • Knowing responsibilities: include knowing about private encapsulated data, knowing about related objects, and knowing about things it can derive or calculate.

GRASP Patterns - Example

• Pattern Name: Information Expert
• Solution: Assign a responsibility to the class that has the information needed to fulfill it.
• Problem it Solves: What is a basic principle by which to assign responsibilities to objects?

GRASP Patterns

• There are nine GRASP patterns:
  • Creator
  • Information Expert (or just Expert)
  • Low Coupling
  • Controller
  • High Cohesion
  • Polymorphism
  • Pure Fabrication
  • Indirection
  • Protected Variations

GRASP Patterns - Creator

• Pattern Name: Creator
• Solution: Assign the responsibility of creating instances of a class to the class that has the most knowledge about when and how to create them.
• Problem: Decide which class should be responsible for creating instances of a new bank account.

GRASP Patterns - Information Expert (or just Expert)

• Pattern Name: Information Expert
• Solution: Assign a responsibility to the class that has the necessary information to fulfill it, promoting high cohesion and minimizing coupling.
• Problem: Determine which class should be responsible for calculating interest on a bank account.

GRASP Patterns - Low Coupling

• Pattern Name: Low Coupling
• Solution: Implement an Observer pattern to notify interested parties (e.g., GUI, Logging module) of changes in bank account balances without tightly coupling them to the BankAccount class.
• Problem: Minimize dependencies between classes to allow for easier maintenance and modification.

GRASP Patterns - Controller

• Pattern Name: Controller
• Solution: Assign the responsibility of handling system events or coordinating activities to a controller class.
• Problem: Determine which class should handle the process of transferring funds between bank accounts.