Reflection with something like class MyClass T extends Date {...}

Question

assume you have:
//first class
class Message {
//second class
class ConcreteMessage extends Message{
//third class
public class WrapperBase<J extends Message> {
    private J message = null;
    public J getMessage() {
        return message;
    public void setMessage(J message) {
        this.message = message;
    public WrapperBase(J message){
        this.message = message;       
//fourth class
class WrapperExtended extends WrapperBase<ConcreteMessage>{
    public WrapperExtended(ConcreteMessage message) {
        super(message);
}Reflecting on the WrapperExtended I obtain the getter(for example)
WrapperExtended ext = new WrapperExtended(message);
Method extMethod =ext.getClass().getMethod("getMessage", new Class[0]);If I check the class of the extMetihd return type I obtain a Message, not a ConcreteMessage as I expected. How can I retrieve the info that the method returns a ConcreteMessage?
Development environment knows that the return type is a ConcreteMessage,so I guess there must me some reflection mechanism to retrieve it.

Answer 1

If I check the class of the extMetihd return type I obtain a Message, not a ConcreteMessage as I expected. How can I retrieve the info that the method returns a ConcreteMessage?
Development environment knows that the return type is a ConcreteMessage,so I guess there must me some reflection mechanism to retrieve it.
Yes, for classs derived from a concrete generic instantiation (such as WrapperBase<String>) you can find the concrete return type via reflection. Here's the code that does the trick:
import java.lang.reflect.Method;
import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Type;
import java.lang.reflect.TypeVariable;
class Message {
//second class
class ConcreteMessage extends Message{
//third class
class WrapperBase<J extends Message> {
    private J message = null;
    public J getMessage() {
        return message;
    public void setMessage(J message) {
        this.message = message;
    public WrapperBase(J message){
        this.message = message;       
    public static Class<?> findConcreteReturnType(Class<? extends WrapperBase<?>> cl, String methodName, Class<?>...params) throws SecurityException, NoSuchMethodException {
         Method extMethod = cl.getMethod(methodName, params);
         if(!(extMethod.getGenericReturnType() instanceof TypeVariable))
              return extMethod.getReturnType();
         TypeVariable<?> genericReturnType = (TypeVariable<?>)extMethod.getGenericReturnType();
         String variableName = genericReturnType.getName();
         ParameterizedType genericSuperclass = (ParameterizedType) cl.getGenericSuperclass();
         TypeVariable<Class<WrapperBase>>[] typeParameters = WrapperBase.class.getTypeParameters();
         for(int i = 0; i < typeParameters.length; ++i) {
              if(typeParameters.getName().equals(variableName)) {
               Type type = genericSuperclass.getActualTypeArguments()[i];
               if(!(type instanceof Class))
                    throw new IllegalArgumentException("class "+cl.getName()+" does not resolve type parameter "+ variableName);
               return (Class<?>)type;
     throw new InternalError();
//fourth class
public class WrapperExtended extends WrapperBase<ConcreteMessage>{
     public WrapperExtended(ConcreteMessage message) {
super(message);
public static void main(String[] args) throws SecurityException, NoSuchMethodException {
          System.out.println(WrapperBase.findConcreteReturnType(WrapperExtended.class, "getMessage"));