Generics in Java

Question

I would like to understand the following type of syntax.

Example:

public interface A < T extends A < T> > {

}

What is the logic of this interface ?

strongly related: http://stackoverflow.com/questions/211143/java-enum-definition — Paul Bellora, Nov 18 '11 at 19:02
also related: http://stackoverflow.com/questions/1563335/recursive-generic-usage — Paul Bellora, Nov 18 '11 at 19:03
related to possible uses: http://stackoverflow.com/questions/7959335/self-bound-generic-type-with-fluent-interface-and-inheritance — Paul Bellora, Nov 18 '11 at 19:08
possible duplicate of [Generics in Java](http://stackoverflow.com/questions/1794842/generics-in-java) — martin clayton, Nov 19 '11 at 15:20

Kerrek SB · Accepted Answer · 2011-11-18T19:14:12.640

This would be used as follows:

class X implements A<X> { /* ... */ }

In other words, you are forced to make the parameter of A the class X itself, and something like class X implements A<Unrelated> is forbidden.

This construction gives the interface access to X through the generic parameter, and the type restriction makes sure that it doesn't get abused. For instance, T can now be assumed to expose all methods that A does.

_{Note that this construction is formally somewhat similar to the curiously recurring template pattern in C++ (although it is technically quite different). In both languages it allows the "base class" to reason about its ultimate derived usage.}

This is a great explanation. I'm wondering though, what are some applications of this other than the `Enum` usage already suggested? A linked list maybe? — flow2k, May 15 '17 at 08:06

Generics in Java

1 Answers1

Linked