How to get Class object of a generic type

Question

I have a static method which will return a custom type based on the type of the class,

public class GenericMethod {

    public static <T> T returnGeneric(Class<T> clazz) {
        return null;
    }

}

Now, I want to pass a class with a generic type in to it,

CustomType<String> type = GenericMethod.returnGeneric(CustomType.class);

Only problem is that the above statement gives and unchecked conversion warning.

I tried the workaround new CustomType<String>().getName() which is also not solving the problem.

Is there a right way to it, or the only solution is to use @SuppressWarnings ?

possible duplicate : http://stackoverflow.com/questions/3403909/get-generic-type-of-class-at-runtime ? — benzonico, Oct 30 '13 at 08:40

score 1 · Accepted Answer · answered Oct 30 '13 at 09:00

1

What you would/should like to try is this:

CustomType<String> type = GenericMethod.returnGeneric(CustomType<String>.class);

Unfortunately, because of type erasure there is no difference between CustomType<A>.class and CustomType<B>.class, hence this syntax is not supported by Java.

So my $.02: what you are asking for is not possible, so hang on to the @suppresswarnings...

answered Oct 30 '13 at 09:00

GerritCap

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Why, as I said: "hence this syntax is not supported by Java" – GerritCap Oct 31 '13 at 08:40

score 1 · Answer 2 · answered Oct 30 '13 at 09:03

1

The best approach is to use a wrapper method and place all your warnings in a single place.

And the term "unchecked" means that the compiler does not have enough type information to perform all type checks necessary to ensure type safety.

answered Oct 30 '13 at 09:03

Ashish

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score 0 · Answer 3 · answered Oct 30 '13 at 09:05

0

In theory you can't do it because of type erasure.

In practice though ;) you can do it because the information is actually in the .class files. The easiest way I know of is using Spring's GenericTypeResolver.

Have a look at it.

answered Oct 30 '13 at 09:05

Simeon

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There is no difference between theory and practice. You are misunderstanding what type erasure is. And class metadata is not relevant to this question. – newacct Oct 31 '13 at 01:56

Sergey Morozov · Answer 4 · 2013-10-30T11:14:39.713

As you said @Simeon "In theory you can't do it because of type erasure". You can use it only if you have subclasses of CustomType:

class GenericMethod {

  public static <T> T returnGeneric(Class<T> clazz) {
    try {
      return  clazz.newInstance();
    } catch (InstantiationException | IllegalAccessException e) {
      e.printStackTrace();
    }
    return null;
  }

  public static void main(String [] args){
    CustomeType<String> ct = returnGeneric(StringCustomeType.class);
    System.out.println(ct);
  }
}

class StringCustomeType extends CustomeType<String> {
}

class CustomeType<T> {
}

How to get Class object of a generic type

4 Answers4