inheritance - Strange interface design Java -

at work came across following design in java project:

consider interfaces foo, bar, , baz follows:

interface bar { public int a(); }

interface baz { public int b(); }

interface foo extends bar, baz { public int c(); }

now, consider class fooimpl:

public class fooimpl implements foo {      private bar bar;     private baz baz;      public int a() {         return bar.a();     }     public int b() {         return baz.b();     }     public int c() {         return 0;     } } 

what use cases kind of class hierarchy? seems me introduces lot of boilerplate , not add in terms of abstraction, other breaking large file smaller files.

it allows things this:

foo foo = new fooimpl(); usebar(foo);  public void usebar(bar bar) {     bar.a(); } 

whether useful depends on real context. example code classes , methods meaningless names not support rational judgement.

the other thing note fooimpl implemented kind of wrapper bar , baz instances. that's not (strictly speaking) interface design issue.