Generics: Creating parameterized class argument

How does one get a parameterized Class object to be used as a method argument?

class A<T>
{
    public A(Class<T> c)
    {
    }

    void main()
    {
        A<String> a1 = new A<String>(String.class);     // OK
        A<List<String>> a2 = new A<List<String>>(List<String>.class);  // error
        A<List<String>> a3 = new A<List<String>>(Class<List<String>>);  // error
    }
}

Why do I want to do that, you may ask? I have a parameterized class whose type is another parameterized class, and whose constructor requires that other class type as an argument. I understand that runtime classes have no information on their type parameters, but that shouldn't prevent me from doing this at compile time. It seems that I should be able to specify a type such as List<String>.class. Is there another syntax to do this?

Here is my real usage case:

public class Bunch<B>
{
    Class<B> type;

    public Bunch(Class<B> type)
    {
        this.type = type;
    }

    public static class MyBunch<M> extends Bunch<List<M>>
    {
        Clas开发者_如何转开发s<M> individualType;

        // This constructor has redundant information.
        public MyBunch(Class<M> individualType, Class<List<M>> listType)
        {
            super(listType);
            this.individualType = individualType;
        }

        // I would prefer this constructor.
        public MyBunch(Class<M> individualType)
        {
            super( /* What do I put here? */ );
            this.individualType = individualType;
        }
    }
}

Is this possible?

---

How about just cast?

super((Class<List<M>>)List.class);

Class literals are not going to have the type parameters that you want.

---

Remember you will NOT get a List as a class in runtime, and the right approach would probably be using TypeToken as BalusC told you. Without TypeToken, you can't cast to List, but you can create something like this:

public static class MyBunch2<List_M extends List<M>, M> extends Bunch<List_M>
{
    Class<M> individualType;

    @SuppressWarnings("unchecked")
        public MyBunch2(Class<M> individualType)
    {
        super((Class<List_M>) List.class);
        this.individualType = individualType;
    }
}

Since List_M extends List<M> this is not as typesafe as you may wish, but maybe is nice enough. Creating an instance will be as ugly as writing

MyBunch2<List<String>, String> a = new MyBunch2<List<String>, String>(String.class);

but you can improve it with a factory method

public static <M2> MyBunch2<List<M2>, M2> of(Class<M2> individualType){
    return new MyBunch2<List<M2>, M2>(individualType);
}

and then write

MyBunch2<List<String>, String> b = MyBunch2.of(String.class);

If you are using eclipse, code assist will help you writing the ugly class MyBunch2, String>

Of course, in runtime, this.type will be java.util.List, not java.util.List To get it right, go for TypeToken.

---Continuation---

You can even make another class

public static class MyBunch3<M> extends MyBunch2<List<M>, M>
{
        public MyBunch3(Class<M> individualType) {
            super(individualType);
        }
}

And then create instances as

MyBunch3<String> c = new MyBunch3<String>(String.class);

There must be a way to do that in just one class...but I can't figure it out