如何使用java反射来实例化一个无法导入的类？

Question

I'm writing JUnit tests to test code in another package which must match a pre-defined specification. The code under test must contains a nested class which I want to instantiate inside the test package -- it's not possible to import this class because it's nested (and so not visible outside the original package).

Eg package structure:

packageA
-> ClassA
     -> packageA.ClassA$ClassB

tests
-> ClassATest

I need to test a method in ClassA that takes an instance of ClassB as an argument.

I'm currently using reflection to get from ClassA (which I can import) to ClassB [ cls.getDeclaredClasses ]. I can then get a constructor for ClassB [ cls.getDeclaredConstructor ] and thus create a new instance of ClassB using the found constructor [ constructor.newInstance ]. This call to constructor.newInstance returns an Object .

How do I get from the returned Object type to something of the correct ClassB type so that I can pass it into the ClassA method under test?

Answer 1

Firstly It is possible to import a nested class. Cannot `import static` static inner class?

This is sounds as a bad design that you are forced to use a reflection for tests.

Because you have got Object from reflection and you don't have a type accessible, you should also use reflection again to pass it into the method.