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Java Generics - Casting to "null's class"

Bob Hunt
Greenhorn

Joined: Mar 26, 2010
Posts: 5
Hi,

I came across an interesting situation.
I've got a method that gets a class as a parameter so the caller method doesn't have to cast, because the called method will have the same return type as the class parameter's type. Here is a simplified version of that.



When I pass I get 10. When I pass "null" I still get 10. When I write I get a compiler error, of course.

My question: What happens when I pass null as a class and the JVM try to cast 10 to null in runtime?
Greg Charles
Sheriff

Joined: Oct 01, 2001
Posts: 2849
    
  11

I don't really know how Java handles null in that case, but I do know it's not at run time. In Java, both casting and generics are seen by the compiler only. They have no effect on the running program.
 
It is sorta covered in the JavaRanch Style Guide.
 
subject: Java Generics - Casting to "null's class"