java Java泛型：使用子类列表设置超类列表
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Java Generics: set List of superclass using List of subclass
提问by Drew Johnson
If I have a method in MyClasssuch as
如果我有一个方法，MyClass例如
setSuperClassList(List<Superclass>)
...should I be able to do this:
...我应该能够做到这一点：
new MyClass().setSuperClassList(new ArrayList<Subclass>())
It appears this won't compile. Why?
看来这不会编译。为什么？
回答by Thomas L?tzer
回答by jjnguy
You are just doing the generics a bit wrong. Add the ? extendsbit, and that will allow the passed in list to contain the SuperClass or any of its subclasses.
你只是在做泛型有点错误。添加该? extends位，这将允许传入的列表包含 SuperClass 或其任何子类。
setSuperClassList(List<? extends Superclass>)
This is called setting an upper bound on the generics.
这称为设置泛型的上限。
The statement List<Superclass>says that the List can only contain SuperClass. This excludes any subclasses.
声明List<Superclass>说列表只能包含SuperClass. 这不包括任何子类。
回答by missingfaktor
回答by Manuel Darveau
Do:
做：
setSuperClassList(List<? extends Superclass> list)
This will allow a list of any subclass of Superclass.
这将允许列出超类的任何子类。
