java - Java中 "methods without access control can be declared more private in subclasses"是什么意思？

Question

在java访问修饰符和继承主题中说了以下4点。第三点中的“更私密”是什么意思？

1. ...
2. ...
3. 声明的方法没有访问控制=>可以在子类中声明更私有(private)
4. ...

Answer 1

Methods declared without access control => can be declared more private in subclasses

这是错误的。情况恰恰相反。使用任何级别的访问控制声明的方法都必须使用该级别或更公共(public)的级别进行覆盖:在这种情况下，访问级别基类是“默认”，因此您可以使用 public 或 进行覆盖> protected 。

与 Google 文档所述相反，您不能使用 private 覆盖。 请参阅 JLS §8.4.8.3 :

The access modifier (§6.6) of an overriding or hiding method must provide at least as much access as the overridden or hidden method, as follows:

• If the overridden or hidden method is public, then the overriding or hiding method must be public; otherwise, a compile-time error occurs.
• If the overridden or hidden method is protected, then the overriding or hiding method must be protected or public; otherwise, a compile-time error occurs.
• If the overridden or hidden method has package access, then the overriding or hiding method must not be private; otherwise, a compile-time error occurs.