java - 为什么我可以用公共(public)方法覆盖 protected 方法？

Question

当我用 public 方法覆盖 protected 方法时，Java 编译器不会报错。这里到底发生了什么？由于父方法的可见性较低，是覆盖还是隐藏了父方法？

Answer 1

子类总是可以扩展访问修饰符，因为它仍然是父类(super class)的有效替代。来自 Java 规范关于 Requirements in Overriding and Hiding :

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 default (package) access, then the overriding or hiding method must not be private; otherwise, a compile-time error occurs.