[筆記] Head First Design Patterns

Chapter 1 Welcome to Design Patterns: an introduction

OO Basics:

• Abstraction
• Encapsulation
• Polymorphism
• Inheritance

OO Principles:

• Encapsulate what varies.
• Favor composition over inheritence.
• Program to interfaces, not implementations.

OO Patterns:

• Strategy - defined a family of algorithms, encapsulates each once, and makes them interchangeable. Strategy lets the algorithm vary independently from clients that use it.

Chapter 2 Keeping your Objects in the know: the Observer Pattern

OO Principles:

• Strive for loosely coupled designs between objects that interact.

OO Patterns:

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

Chapter 3 Decorating Objects: the Decorator Pattern

OO Principles:

• Classes should be open for extension but closed for modification.

OO Patterns:

• Decorator - Attach additional responsibilities to an object dynamically. Decorators provide a flexible alternative to subclassing for extending functionality.

Chapter 4 Baking with OO Goodness: the factory Pattern

OO Principles:

• Depend on abstractions. Do not depend on concrete classes.

OO Patterns:

• Abstract Factory - Provide an interface for creating families of related or dependent objects without specifying their concrete classes.
• Factory Method - Define an interface for creating an object, but let subclasses decide which class to instantiate. Factory Method lets a class defer instantiation to the subclasses.

Chapter 5 One of a Kind Objects: the Singleton Pattern

OO Patterns:

• Singleton - Ensure a class only has one instance and provide a global point of access to it.

Chapter 6 Encapsulating Invocation: the Command Pattern

OO Patterns:

• Command - Encapsulates a request as an object, thereby letting you parameterize other objects with different requests, queue or log requests, and support undoable operations.

When you need to decouple an object making requests from the objects that know how to perform the requests, use the Command Pattern.

Chapter 7 Being Adaptive: the Adapter and Facade Patterns

OO Principles:

• Only talk to your fiends

OO Patterns:

• Adapter - Converts the interface of a class into another interface clients expect. Lets classes work together that couldn't otherwise because of incompatible interfaces.
• Facade - Provides a unified interface to a set of interfaces in a subsystem. Facade defined a higher-level interface that makes the subsystem easier to use.

Chapter 8 Encapsulating Alogrithms: the Template Method Pattern

OO Principles:

• Don't call us, we'll call you.

OO Patterns:

• Template Method - Defined the skeleton of an algorithm in an operation, deferring some steps to subclasses. Template Method lets subclasses redefine certain steps of an algorithm without changing the algorithm's structure.

Chapter 9 Well-Managed Collections: the Iterator and Composite Patterns

OO Patterns:

• Iterator - Provide a way to access the elements of an aggregate object sequentially without exposing its underlying representation.
• Composite - Compose objects into tree structures to represent part-whole hierarchies. Composite lets clients treat individual objects and compositions of objects uniformly.

Chapter 10 The State of Things: the State Pattern

OO Pattern:

• State - Allows an object to alter its behavior when its internal state changes. The object will appear to change it class.

Chapter 11 Controlling Object Access: the Proxy Pattern

OO Pattern:

• Proxy - Provide a surrogate or placeholder for another object to control access to it.

Chapter 12 Patterns of Patterns: Compound Patterns

OO Pattern:

• Compound Patterns - A Compound Pattern combines two or more patterns into a solution that solves a recurring or general problem.

Chapter 13 Patterns in the Real World: Better Living with Patterns

Chapter 14 Appendix: Leftover Patterns

OO Patterns:

• Bridge - Use the Bridge Pattern to vary not only your implementations, but also your abstractions.
• Builder - Use the Builder Pattern to encapsulate the construction of a product and allow it to be constructed in steps.
• Chain of Responsibility - Use the Chain of Responsibility Pattern when you want to give more than one object a chance to handle a request.
• Flyweight - Use the Flyweight Pattern when one instance of a class can be used to provide many "virtual instances."
• Interpreter - Use the Interpreter Pattern to build an interpreter for a language.
• Mediator - Use the Mediator Pattern to centralize complex communications and control between related objects.
• Memento - Use the Memento Pattern when you need to be able to return an object to one of its previous states; for instance, if your use requests an "undo."
• Prototype - Use the Prototype Pattern when creating an instance of a given class is either expensive or complicated.
• Visitor - Use the Visitor Pattern when you want to add capabilities to a composite of objects and encapsulation is not important.