Why use method local abstract inner classes

Question

One of the legal modifiers you can use with method local inner classes is abstract.

For example:

public class Outer {
    public void method(){
        a         


        

Answer 1

the only real use I can imagine is for nodes in a data structure

that way you can differentiate methods from sentinel nodes and normal data nodes which can be really handy in recursive algorithms and you don't have to null check each time