Question

With generic methods it’s possible to extend more than one type, e.g.:

<T extends MyClass & MyInterface> void foo(T bar)

Is there a way to specify a List with a parameter which extends more than one type?

List<MyClass & MyInterface> myList;

doesn’t work…

This would allow the following:

class A extends MyClass implements MyInterface{}

class B extends MyClass implements MyInterface{}

myList.add(new A());
myList.add(new B());

MyClass c = myList.get(index);
MyInterface i = myList.get(index);

foo(myList.get(index));

Answer 1

The answer is NO.

Depending on your semantic expectation you will find a workaround

One possible workaround for foo

   <T extends MyClass> void foo(T bar) {
     if (bar instanceof MyInterface) return;
   }

Probably the best approach is to create a type supplying both type.
The drawback is, all interesting classes needs to derived from that class

abstract class MyClassInterface extends MyClass implements MyInterface {}

List<MyClassInterface> myList;


<T extends MyClassInterface> void foo(T bar)

The naive approach just to supply both methods will cause ambiguities, so it is not a possible (for “AND”, for “XOR” it would be valid)

<T extends MyClass> void foo(T bar)

<T extends MyInterface> void foo(T bar)