How do I get the `.class` attribute from a generic type parameter?

Question

The accepted answer to this question describes how to create an instance of T in the Generic class. This involves passing in a Class<

Answer 1

W may not be available due to type erasure. You should require that a Class<W> is passed into the method. You get a class object and its generic ensures that only W and no subclass is passed in, due to covariance.

public InputField(String labelText, Class<W> cls)
{
    super(new String[] {labelText}, cls);
}

will take W.class but not WSubtype.class.

Answer 2

Using .class on a type parameter isn't allowed - because of type erasure, W will have been erased to Component at runtime. InputField will need to also take a Class<W> from the caller, like InputFieldArray:

public InputField(String labelText, Class<W> clazz)
{
    super(new String[] {labelText}, clazz);
}

Answer 3

If you're using the GSON library, you can get the type of T easily by using TypeToken. The class documentation is available here:

I did it like this:

This is my class definition:

public class ManagerGeneric <T> {}

This is in my method:

// Get the type of generic parameter
Type typeOfT = new TypeToken<T>(){}.getType();
// Deserialize
T data = gson.fromJson(json, typeOfT);