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README
Apache-2.0

design-pattern

介绍

设计模式的介绍、使用案例及在源码中的使用场景

模块说明

使用设计模式的目的

  1. 代码重用性 (即:相同功能的代码,不用多次编写)
  2. 可读性 (即:编程规范性, 便于其他程序员的阅读和理解)
  3. 可扩展性 (即:当需要增加新的功能时,非常的方便,称为可维护)
  4. 可靠性 (即:当我们增加新的功能后,对原来的功能没有影响)
  5. 使程序呈现高内聚,低耦合的特性

设计模式的核心思想

  1. 找出应用中可能需要变化之处,把它们独立出来,不要和那些不需要变化的代码混在一起
  2. 针对接口编程,而不是针对实现编程
  3. 为了交互对象之间的松耦合设计而努力

设计模式的七大原则

  1. 单一职责原则
    1. 降低类的复杂度,一个类只负责一项职责。
    2. 提高类的可读性,可维护性
    3. 降低变更引起的风险
    4. 通常情况下,我们应当遵守单一职责原则,只有逻辑足够简单,才可以在代码级违反单一职责原则;只有类中方法数量足够少,可以在方法级别保持单一职责原则
  2. 接口隔离原则
    1. 客户端不应该依赖它不需要的接口,即一个类对另一个类的依赖应该建立在最小的接口上
    2. 类A通过接口Interface1依赖类B,类C通过接口Interface1依赖类D,如果接口Interface1对于类A和类C来说不是最小接口,那么类 B 和类 D 必须去实现他们不需要的方法
    3. 将接口 Interface1 拆分为独立的几个接口(这里我们拆分成 3 个接口),类 A 和类 C 分别与他们需要的接口建立 依赖关系。也就是采用接口隔离原则
  3. 依赖倒转原则
    1. 高层模块不应该依赖低层模块,二者都应该依赖其抽象
    2. 抽象不应该依赖细节,细节应该依赖抽象
    3. 依赖倒转的中心思想是面向接口编程
    4. 依赖倒转原则是基于这样的设计理念:相对于细节的多变性,抽象的东西要稳定的多,以抽象为基础搭建的架构比以细节为基础的架构要稳定的多。在 java 中,抽象指的是接口或抽象类,细节就是具体的实现类
    5. 使用接口或抽象类的目的是制定好规范,而不涉及任何具体的操作,把展现细节的任务交给他们的实现类去完成
  4. 里氏替换原则
    1. 如果对每个类型为 T1 的对象 o1 ,都有类型为 T2 的对象 o2 ,使得以 T1 定义的所有程序P在所有的对象 o1 都代换成 o2 时,程序 P 的行为没有发生变化,那么类型 T2 是类型 T1 的子类型。换句话说,所有引用基类的地方必须能透明地使用其子类的对象
    2. 在使用继承时,遵循里氏替换原则,在子类中尽量不要重写父类的方法
    3. 里氏替换原则告诉我们,继承实际上让两个类耦合性增强了,在适当的情况下,可以通过聚合,组合,依赖来解决问题
  5. 开闭原则
    1. 开闭原则(OpenClosedPrinciple)是编程中最基础、最重要的设计原则
    2. 一个软件实体如类,模块和函数应该对扩展开放(对提供方),对修改关闭(对使用方)。用抽象构建框架,用实现扩展细节
    3. 当软件需要变化时,尽量通过扩展软件实体的行为来实现变化,而不是通过修改已有的代码来实现变化
    4. 编程中遵循其它原则,以及使用设计模式的目的就是遵循开闭原则
  6. 迪米特法则
    1. 一个对象应该对其他对象保持最少的了解
    2. 类与类关系越密切,耦合度越大
    3. 迪米特法则(DemeterPrinciple)又叫最少知道原则,即一个类对自己依赖的类知道的越少越好。也就是说,对于被依赖的类不管多么复杂,都尽量将逻辑封装在类的内部。对外除了提供的 public 方法,不对外泄露任何信息
    4. 迪米特法则还有个更简单的定义:只与直接的朋友通信
    5. 直接的朋友:每个对象都会与其他对象有耦合关系,只要两个对象之间有耦合关系,我们就说这两个对象之间 是朋友关系。耦合的方式很多,依赖,关联,组合,聚合等。其中,我们称出现成员变量,方法参数,方法返 回值中的类为直接的朋友,而出现在局部变量中的类不是直接的朋友。也就是说,陌生的类最好不要以局部变 量的形式出现在类的内部
  7. 合成复用原则
    1. 尽量使用合成/聚合的方式,而不是使用继承

设计模式的类型

  1. 创建型模式: 单例模式、抽象工厂模式、原型模式、建造者模式、工厂模式
  2. 结构型模式: 适配器模式、桥接模式、装饰模式、组合模式、外观模式、享元模式、代理模式
  3. 行为型模式: 模版方法模式、命令模式、访问者模式、迭代器模式、观察者模式、中介者模式、备忘录模式、 解释器模式、状态模式、策略模式、职责链模式(责任链模式)
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