Getting the Class object of a generic type

[Hopea Tassu]

Is it possible to get and store the type of a generic variable somehow like you can use the class literal String.class?

   
public <T>void foo(T var) {
//Class c = T.class?
}
 

If the method is called as <String>, the variable c should contain String.class.

[Bear Bibeault]

It is not possible.

[Rob Spoor]

And the reason is type erasure. Look it up.

Unfortunately, var.getClass() won't help you either, and the following example shows why:

Object o = "Hello World";
foo(o);
// inside foo, var.getClass() will not be Object.class but String.class

Because of polymorphism and interfaces, you can never say that calling getClass() on a reference with type X will return Class<X>.

[Campbell Ritchie]

Welcome to JavaRanch

To elaborate on what Bear has told you: Java does generics by type erasure, so the actual type parameter <String> vanishes entirely at runtime. You can identify the type of one of the elements of a Collection, but that is not necessarily the same as the type of the actual type parameter.

Simpler tutorial here.