Interface defined inside a class

Question

How to indicate that an interface is a part of class? Let's take this case as an example.

public class Function
{
     public interface Function2D
     {
            double GetValue(double x);
     }

     ...

}

Talking more precisely - I need to show the relationship between Function and Function2D in an UML class diagram.

What do you accomplish by declaring `Function2D` inside `Function`? — Jim Garrison, May 02 '13 at 21:21
This is not the usual java-way of doing it, but if you do so, you have to implement it like : `public class MyImplementation implements Function.Function2D`. — Bjørn Bråthen, May 02 '13 at 21:30
I do not see any field. Just a method declaration. And an interface can have final static fields. — Jean Waghetti, May 02 '13 at 21:33
@JimGarrison: it's a technique that allows to relieve function pointers in JAVA. — 0x6B6F77616C74, May 02 '13 at 21:37
A nested interface isn't "part of a class". A class either conforms to an interface or it does not. If it is *just* nested - e.g. as with a static inner class - then *there is no relationship between types*; there might be scoping rules which makes the only valid relationships internal to the class, but .. [refer to this answer](http://stackoverflow.com/a/74400/2246674) — user2246674, May 02 '13 at 21:40
Doesn't the java compiler translate this interface to a top level one? i'm I right? — Bjørn Bråthen, May 02 '13 at 21:41
The "functor" pattern does not require that you declare an "inner" interface. — Jim Garrison, May 02 '13 at 21:43

score 2 · Accepted Answer · edited Sep 02 '19 at 21:29

2

This UML Quick Reference gives an indication of how to represent an Inner class in a UML diagram:

edited Sep 02 '19 at 21:29

Glorfindel

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answered May 02 '13 at 21:32

femtoRgon

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How would an inner *static* class (that isn't used) be represented? Interfaces are like [static nested classes](http://stackoverflow.com/a/70358/2246674) (not to be confused with inner classes) in that they do not imply a binding with the parent type. – user2246674 May 02 '13 at 21:43
They're bound to parent class, not parent class object instance. – Jean Waghetti May 02 '13 at 21:47
@JeanWaghetti Why are they "bound"? What happens if the only creation/usage of such (interface type) happens from *outside* the class they are nested in? Is it accurate to still view such having any meaningful relationship? I feel that the relationships in the presented code cannot be sensibly stated. Perhaps the outer class could be viewed as a container (e.g. a package), if such UML diagram is simply showing relationships between naming containers. – user2246674 May 02 '13 at 21:47
The question is about inner interface. Should the lines be dashed? – 0x6B6F77616C74 May 02 '13 at 21:55
Well, it can not make sense. The same way a static inner class could not make sense. But it exists and have it's usage. (I'm not saying an inner static class does not make sense to me. It does. But when's was introduced to them, it took a while to understand them). – Jean Waghetti May 03 '13 at 02:52
@0x6B6F77616C74: The lines should not be dashed. The dashed line is only for interface realizations. This is a containment edge. – Carsten May 03 '13 at 08:16
1

@user2246674: That's exactly what the containment signifies here - the inner class uses the outer class as its namespace, much like another class has a package as its namespace. – Carsten May 03 '13 at 08:19

Interface defined inside a class

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