抽象有什么用? [英] What is the use of Abstraction?

问题描述

我正在努力理解抽象在 Java 中的整体使用.

I'm struggling to understand the overall use of Abstraction in Java.

我一直在研究此链接中的一个示例:https://javatutorial.net/java-抽象例子我理解它的实现，但我不明白为什么它甚至是必要的.如果他们只是要在 2 个子类中再次创建，为什么他们的一个 calculateSalary 方法是在 Employee 类中创建的?

I have been working off an example in this link: https://javatutorial.net/java-abstraction-example I understand the implementation of it but I don't understand why its even necessary. Why is their a calculateSalary method made in the Employee class if they are just going to made again in the 2 subclasses?

推荐答案

抽象的整体使用是解耦的.要使用 Employee，不需要知道实现，只需要知道接口和它的契约.例如，这用于 Collections.sort(List list):Collections.sort(...) 无需知道特定列表的实现即可对其进行排序.这提供了实现支持符合 List 界面.这个问题在这方面是相关的(#selfPromotion).更少的耦合导致更少的摩擦和整体更不脆弱的代码.

The overall use of abstraction is decoupling. To work with an Employee, one does not need to know the implementation, only the interface and its contracts. This is, for example, used for Collections.sort(List<T> list): the programmers of Collections.sort(...) did not need to know the implementation of a specific list in order to sort it. This provides the benefit that the implementation support future code that conforms to the List interface. This question is related in that respect (#selfPromotion). Less coupling leads to less friction and overall less fragile code.

也就是说，您提供的示例很糟糕，因为它违反了单一职责原则:计算薪水不是Employee实例的责任.为此，我们应该有一个单独的对象来计算工资，基于 Employee 实例和一些工作时间.在内部，这个 Uber 计算器可以使用一个责任链，其中包含一个Calculator per Employee - 实施，将 Employee 与他们的工资计算方式分离.这提供了可扩展性和灵活性的额外好处:如果计算薪水的方式发生变化(例如，公司可能会更改政策，以便每个 FullTimeEmployee 获得相同的薪水，或者公司可能想要计算薪水按周而不是按月)，使用 FullTimeEmployee 的其他服务表示不受影响).

That said, the example you provided is a poor one since it violates the Single Responsibility Principle: It is not the responsibility of an Employee instance to calculate the salary. For this, we should have a separate object that calculates the salary, based on an Employee-instance and some hours worked. Internally, this Uber-calculator could use a Chain of Responsibility, which hold one Calculator per Employee-Implementation, decoupling the Employee from how their salary is calculated. This provides the added benefit of extensibility and flexibility: if the way a salary is calculated changes (e.g. maybe the company switches policy so that each FullTimeEmployee earns the same salary, or maybe the company wants to calculate the salary on a by-week instead of a by-month basis), other services using the FullTimeEmployee say unaffected).

这篇关于抽象有什么用?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！