How to read class types of generics parameters using Java reflection

Question

I have a class BaseClass<X, Y, Z>. And I implement the class as SuperCar implements BaseClass<Color, Engine, Foo>. So now i need to get those X,Y,Z values by using reflection on SuperCar class. Is this possible ?

I guess it is not possible, remember that Java generics use erasure, the type parameters are "forgotten" after compilation. E.g. ArrayList<Car> is compiled to ArrayList<Object> - compiler doesn't compile if you try to put a Helicopter in ArrayList<Car>, but the runtime only sees ArrayList<Object> and would happily allow it. — marek.jancuska
– marek.jancuska, Commented Mar 19, 2015 at 14:46
There is a excellent answer on this post to explain how to do this. stackoverflow.com/questions/1901164/… — APD
– APD, Commented Mar 19, 2015 at 14:52

Konstantin Yovkov · Accepted Answer · 2015-03-19 14:48:08Z

1

You can inspect the type parameters for the superclass, having the Class of the SuperCar:

SuperCar car = new SuperCar();
ParameterizedType parameterizedType = (ParameterizedType) car.getClass().getGenericSuperclass();
Type[] superClassTypes = parameterizedType.getActualTypeArguments();
for (Type type : superClassTypes) {
    System.out.println(type.getTypeName());
}

This should give you:

Color
Engine
Foo

answered Mar 19, 2015 at 14:48

Konstantin Yovkov

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Pinguin895 · Accepted Answer · 2015-03-19 14:53:41Z

1

i guess you want to have something like this:

ParameterizedType types = (ParameterizedType) SuperCar.class.getGenericInterfaces()[0];
for (Type type : types.getActualTypeArguments()) {
    Class<?> cl = (Class<?>) type;
    System.out.println(cl.getName());
}

instead of printing the name you can do whatever you like with it

answered Mar 19, 2015 at 14:53

Pinguin895

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