Java generics seem to work differently for classes than for methods

Question

I'm following this:

http://rickyclarkson.blogspot.com/2006/07/duck-typing-in-java-and-no-reflection.html

And I'm trying to adapt this:

<T extends CanQuack & CanWalk> void doDucklikeThings(T t)
{
    t.quack();
    t.walk();
}

To this:

public class Activate<D extends CanQuack & CanWalk> {

    D d = new MyWaterFowl(); //Type mismatch
}

Even though MyWaterFowl implements those interfaces.

I'd like a solution that never mentions MyWaterFowl in the <>'s since I'm going to eventually just be injecting it (or anything else that implements those interfaces).

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If your answer is basically "You can't do that, what type would it even be?". Please explain why it's working for the method doDucklikeThings and conclusively state if it is impossible to do the same with a class or, if it is possible, how to do it.

The T in doDucklikeThings must be something valid since it's working. If I passed that into a class what would I be passing in?

---

As requested here's the MyWaterFowl code:

package singleResponsibilityPrinciple;

interface CanWalk { public void walk(); }
interface CanQuack { public void quack(); }
interface CanSwim { public void swim(); }


public class MyWaterFowl implements CanWalk, CanQuack, CanSwim {

    public void walk() { System.out.println("I'm walkin` here!"); }
    public void quack() { System.out.println("Quack!"); }
    public void swim() { System.out.println("Stroke! Stroke! Stroke!"); }
}

Remember I've confirmed that doDucklikeThings works. I need the syntax that will let me inject anything that implements the required interfaces.

Answer 1

This does not work, because the class/method is generic and the caller of your class/method can set D to MyAmericanEagle.

 Activate<MyAmericanEagle> active = new Activate<>();

Then your code would result in

 MyAmericanEagle d = new MyWaterFowl(); 

Since that makes no sense (would result in ClassCastException) the compiler rejects it.