关于java密封类限制父类和子类只能在一个包下

Z时代
2024-02-17
分类：IT

比如：
原本子类在service/impl包下
父类在service包下。
而密封类限制父类和子类只能在一个包下，
那么密封类不能用于这样的模式了？

回答：

并不一定非得在同一个包下。

Java 规范原文：

REF: JEP-360 Sealed Classes:
A sealed class imposes three constraints on its permitted subclasses (the classes specified by its permits clause):
The sealed class and its permitted subclasses must belong to the same module, and, if declared in an unnamed module, the same package.
Every permitted subclass must directly extend the sealed class.
Every permitted subclass must choose a modifier to describe how it continues the sealing initiated by its superclass:
A permitted subclass may be declared final to prevent its part of the class hierarchy from being extended further.
A permitted subclass may be declared sealed to allow its part of the hierarchy to be extended further than envisaged by its sealed superclass, but in a restricted fashion.
A permitted subclass may be declared non-sealed so that its part of the hierarchy reverts to being open for extension by unknown subclasses. (A sealed class cannot prevent its permitted subclasses from doing this.)

注意加粗部分。