java - How to put a static variable in a parent Object that is different between different children in Java

Question

Conider I have a Class called Entity that has 3 children :
ClientEntity, EmployeeEntity and ProductEntity
I want to have a static attribute _nextId (that gives the new id for a new record) _nextId has a different value in each entity, but its a common attribute to all Entity children.

So my question is how can I put _nextId in Entity class and have methods that change this value, while getting a different value for each child class.

Thank you.

Answer 1

假设Entity是抽象的，您可以创建一个：

protected abstract getNextId();

每个具体子类都需要实现的方法。例如，该实现可以依赖于静态计数器。

Answer 2

你将不得不隐藏它。这意味着您也需要在子类中具有相同的变量。

如果你在超类中声明一个静态变量，所有子类都会访问同一个变量，直到它们通过自己声明一个同名的变量来隐藏它。