Is it possible to write a Java interface from which you could create an anonymous class, but for which you can't create a lambda expression?

Question

Is it possible to write a Java interface from which you could create an anonymous class, but for which you can't create a lambda expression?

Why or why not???

Answer 1

Lambda expressions can only be used to implement functional interfaces, i.e. interfaces with exactly one abstract method.

JLS 15.27. Lambda Expressions says:

Evaluation of a lambda expression produces an instance of a functional interface (§9.8).

JLS 9.8. Functional Interfaces says:

A functional interface is an interface that has just one abstract method (aside from the methods of Object), and thus represents a single function contract.

So if you want a Java interface for which you can't create a lambda expression, make the interface have 2 or more abstract methods.

Anonymous classes can still implement such an interface, because they support implementation of more than one method.