Why would a static nested interface be used in Java? -

i have found static nested interface in our code-base.

class foo {     public static interface bar {         /* snip */     }     /* snip */ } 

i have never seen before. original developer out of reach. therefore have ask so:

what semantics behind static interface? change, if remove static? why this?

the static keyword in above example redundant (a nested interface automatically "static") , can removed no effect on semantics; recommend removed. same goes "public" on interface methods , "public final" on interface fields - modifiers redundant , add clutter source code.

either way, developer declaring interface named foo.bar. there no further association enclosing class, except code cannot access foo not able access foo.bar either. (from source code - bytecode or reflection can access foo.bar if foo package-private!)

it acceptable style create nested interface way if expect used outer class, not create new top-level name. example:

public class foo {     public interface bar {         void callback();     }     public static void registercallback(bar bar) {...} } // ...elsewhere... foo.registercallback(new foo.bar() {     public void callback() {...} });