How to get concrete type of a generic interface

Question

I have an interface

public interface FooBar<T> { } 

I have a class that implements it

public class BarFoo implements FooBar<Person> { }

With reflection, I want to take an instance of BarFoo and get that the version of FooBar it implements is Person.

I use .getInterfaces from BarFoo to get back to FooBar, but that doesn't help me find out what T is.

Answer 1

You can grab generic interfaces of a class by Class#getGenericInterfaces() which you then in turn check if it's a ParameterizedType and then grab the actual type arguments accordingly.

Type[] genericInterfaces = BarFoo.class.getGenericInterfaces(); for (Type genericInterface : genericInterfaces) {     if (genericInterface instanceof ParameterizedType) {         Type[] genericTypes = ((ParameterizedType) genericInterface).getActualTypeArguments();         for (Type genericType : genericTypes) {             System.out.println("Generic type: " + genericType);         }     } } 

Answer 2

Try something like the following:

Class<T> thisClass = null; Type type = getClass().getGenericSuperclass(); if (type instanceof ParameterizedType) {     ParameterizedType parameterizedType = (ParameterizedType) type;     Type[] typeArguments = parameterizedType.getActualTypeArguments();     thisClass = (Class<T>) typeArguments[0]; }