How to import two classes with the same name in di

问题:

I want to import these two classes, both named Query - one a JDO class, the other a JPA class, to use in different methods in the same class.

import javax.jdo.Query;
import javax.persistence.Query;

Is there a way to globally import both of them at the same time at the top of the file?

回答1:

I'm afraid, no. But you don't have to import class to use it: just reference one of the classes by its full name, like

javax.jdo.Query query = getJDOQuery();
query.doSomething();

Then you can import another without name collisions.

BTW, sometimes if you start getting lots of such name such collisions in your class, it's a subtle hint for refactoring: splitting functionality of one big class between several small ones.

回答2:

The only purpose of an import statement is to establish a shorthand alias for a fully-qualified name. If you were allowed to imported both, you'd create an ambiguity that would require type inference to resolve, and make your code extremely difficult to read.

回答3:

The existing answers are correct. I'd like to show you how class name conflicts can be handled in Kotlin (docs).

If there is a name clash, we can disambiguate by using as keyword to locally rename the clashing entity:

import javax.jdo.Query // Query is accessible
import javax.persistence.Query as jpaQuery // jpaQuery stands for 'javax.persistence.Query'

That's +1 reason why you should consider Kotlin for your next project.