Access class name of parameterized type

Question

I have a parameterized class. I would like to get the name of the class represented by the class name. For instance, what I want to do is this:

public T foo(){
    System.out.println(T.class.getName());
}

http://stackoverflow.com/questions/3403909/get-generic-type-of-class-at-runtime possible duplicate — narek.gevorgyan, Jan 23 '12 at 14:10

score 2 · Answer 1 · answered Jan 23 '12 at 14:10

2

You can't do it this way, since T isn't known at compile time. You could achieve something similar like so:

public void foo(T t) {
    System.out.println(t.getClass().getName());
}

Note that this takes an instance of T and would print out the name of its dynamic type.

Whether or not this is a good enough substitute depends on your use case.

answered Jan 23 '12 at 14:10

NPE

In addition, this gives you the name of the class of `t`, which could be a subclass of the type parameter. – Stephen C Jan 23 '12 at 14:16
@StephenC: This is what I meant by "*dynamic* type". – NPE Jan 23 '12 at 14:19

score 1 · Accepted Answer · answered Jan 23 '12 at 14:10

1

Java generics don't work that way. If you have any bounds on T, you can access the bounds by querying the type variable definition. E.g.:

public class Foo<T extends Bar>{}

will let you get at Bar, but not at the subtype of Bar you are actually using. It doesn't work, sorry.

Read the Java Generics FAQ for more info.

BTW: One common solution to this problem is to pass the subtype of T into your class, e.g.

public T foo(Class<? extends T> tType){
    System.out.println(tType.getName());
}

I know it's cumbersome, but it's all Java generics allow.

answered Jan 23 '12 at 14:10

Actually, you can get what `T` is. See my answer for how. (Not sure why it was downvoted!) – ziesemer Jan 24 '12 at 01:18
@ziesemer you can only get at bounds that are actually there. If the above T was declared `T extends Something`, you could get at the something part. But if your type variables have no bounds there's nothing to get at. – Sean Patrick Floyd Jan 24 '12 at 07:30

score 0 · Answer 3 · answered Jan 23 '12 at 14:10

0

public T foo(T t){
    System.out.println(t.getClass().getName());
}

answered Jan 23 '12 at 14:10

Bhesh Gurung

3 Answers3