code: public static boolean isPublicMethodFinal(Class clazz, String name,
                                                TypeDesc retType, TypeDesc[] params)
      {
          if (!clazz.isInterface()) {
              Class[] paramClasses;
              if (params == null || params.length == 0) {
                  paramClasses =  null;
              } else {
                  paramClasses = new Class[params.length];
                  for (int i=0; i<params.length; i++) {
                      paramClasses[i] = params[i].toClass();
                  }
              }
              try {
                  Method existing = clazz.getMethod(name, paramClasses);
                  if (Modifier.isFinal(existing.getModifiers())) {
                      if (retType == null) {
                          retType = TypeDesc.forClass(void.class);
                      }
                      if (TypeDesc.forClass(existing.getReturnType()) == retType) {
                          // Method is already implemented and is final.
                          return true;
                      }
                  }
              } catch (NoSuchMethodException e) {
              }
          }
  
          return false;
      }
docs: Returns true if a public final method exists which matches the given
  specification.