【创建模式-构建模式（Singleton Pattern）】

Overview

The Builder design pattern is one of the GoF design patterns that describe how to solve recurring design problems in object-oriented software.
构建者设计模式是四人帮的设计模式中的一种，《设计模式》一书旨在阐述如何解决面向对象软件开发中反复出现的设计问题。

The Builder design pattern solves problems like
《设计模式》解决如下类似问题：

How can a class (the same construction process) create different representations of a complex object?
How can a class that includes creating a complex object be simplified?
Creating and assembling the parts of a complex object directly within a class is inflexible.
It commits the class to creating a particular representation of the complex object and makes it impossible to change the representation later independently from (without having to change) the class.

The Builder design pattern describes how to solve such problems:

Encapsulate creating and assembling the parts of a complex object in a separate Builder object.
A class delegates object creation to a Builder object instead of creating the objects directly.
A class (the same construction process) can delegate to different Builder objects to create different representations of a complex object.

Definition
The intent of the Builder design pattern is to separate the construction of a complex object from its representation. By doing so, the same construction process can create different representations.[1]

Advantages
Advantages of the Builder pattern include:[3]

Allows you to vary a product’s internal representation.
Encapsulates code for construction and representation.
Provides control over steps of construction process.
Disadvantages
Disadvantages of the Builder pattern include:[3]

Requires creating a separate ConcreteBuilder for each different type of product.
Requires the builder classes to be mutable.
Dependency injection may be less supported.