java访问修饰符和重写方法 [英] java access modifiers and overriding methods

问题描述

为什么Java指定覆盖方法的访问说明符可以允许比重写方法更多但不是更少的访问？例如，超类中的受保护实例方法可以在子类中公开，但不是私有的。

Why does Java specify that the access specifier for an overriding method can allow more, but not less, access than the overridden method? For example, a protected instance method in the superclass can be made public, but not private, in the subclass.

推荐答案

这是一个OOP中的基本原则：子类是父类的完全成熟实例，因此必须至少提供与父类相同的接口。使受保护/公共事物不那么明显会违反这一想法;你可以让子类无法用作父类的实例。

It's a fundamental principle in OOP: the child class is a fully-fledged instance of the parent class, and must therefore present at least the same interface as the parent class. Making protected/public things less visible would violate this idea; you could make child classes unusable as instances of the parent class.

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