How can I use reflection to build generic subtypes?

Question

I'm using the Factory pattern to hide some instance creation complexity. I have this:

class FooInt extends Foo<int>;

I want to do:

class<Foo<?>> fooType = FooInt.class;

All derived types of Foo have a single constructor taking 2 arguments. So I need to use reflection to create instances of subtypes:

Constructor<Foo<?>> ctor = fooType.getContructor(Blah.class, Blahblah.class);
return ctor.newInstance(blah, blahblah);

But javac says:

"Type mismatch: cannot convert from Class<FooInt> to Class<Foo<?>>"

What am I doing wrong? Is it possible to use reflection this way?

Answer 1

try: Class<? extends Foo<?>> fooType = FooInt.class;

One other point is:

• the Class Type is Class not class (upper case C);
• you can not use primities in generics (use Integer instead of int)

---

Added: and this is how it works:

public class Foo<T> {

    private T value;

    public Foo(T value) {    
        this.value = value;
    }      
}

public class FooInt extends Foo<Integer>{
    public FooInt(Integer value) {
        super(value);
    }
}

public class FooDouble extends Foo<Double>{
    public FooDouble(Double value) {
        super(value);
    }
}

The factory (at least only one line, but a lot of exceptions ;-) ):

import java.lang.reflect.InvocationTargetException;

public class Factory {

    <P, T extends Foo<P>> T build(Class<T> clazz, P param)
            throws IllegalArgumentException, SecurityException,
               InstantiationException, IllegalAccessException,
               InvocationTargetException, NoSuchMethodException {
        return clazz.getConstructor(param.getClass()).newInstance(param);
    }

    public static void main(String[] args)
            throws IllegalArgumentException, SecurityException,
                InstantiationException, IllegalAccessException,
                InvocationTargetException, NoSuchMethodException {

        Factory f = new Factory();

        System.out.println(f.build(FooInt.class, Integer.valueOf(1)));
        System.out.println(f.build(FooDouble.class, Double.valueOf(1.1)));
    }
}