Design-Patterns-Example

Open Source examples for the different design patterns. The examples provided are all java based on patterns and they're inspired by the book Head First Design Pattern

OO Basics

• Abstraction
• Encapsulation
• Polymorphism
• Inheritance

OO Principles

• Encapsulates what varies
• Favor composition over inheritance
• Program to interfaces, not implementations
• Strive for loosely coupled designs between objects that interact

OO Patterns

Strategy Pattern

Defines a family of algorithms, encapsulates each one and makes them interchangeable. Strategy lets the algorithm vary independently from clients that use it.

Observer Pattern

defines a one-to-many dependency between objects so that all its dependents are notified and updated automatically when one object changes state.

• The observer Pattern defines a one-to-many relationship between objects
• Subjects, or as we know them, Observables, update Observers using a common interface.
• Observers are loosely coupled in that the Observable knows nothing about them, other than that they implement the Observer Interface.
• Push or pull data from the Observable can be done when using the pattern (pull is considered more “correct”).
• Don’t depend on a specific order of notification for the Observers.
• Java has several implementations of the Observer Pattern, including the general purpose java.util.Observable.
• Watch out for issues with the java.util.Observable implementation.
• Don’t be afraid to create an Observable implementation if needed.
• Swing makes heavy use of the Observer Pattern, as do many GUI frameworks. It can also be found in many other places, including JavaBeans and RMI.