Enforcing return type for an class that implements an interface

Question

How do I enforce that the method getFoo() in the implementing class, returns a list of the type of same implementing class.

public interface Bar{
     ....
          


        

Answer 1

This is not possible in Java, but you might wonder what the use-case is to force this in the interface.

• If you program against the interface (which you typically do, why else define the interface) the type wouldn't be known
• If you program against a specific class, this thread already provided options on how you can implement that specific class to return a List. And since you program against that specific class, the compiler has access to that specific return type and knows about it