why an summary category implementing an interface skip declaration/implementation interface's methods?

a extraordinary thing happens java an summary category exercise an interface: interface's methods totally blank (i.e. conjunction an summary chapter an tangible doing present), nonetheless compiler does complain.

for example, given interface:

public interface ianything {
  vacant m1();
  vacant m2();
  vacant m3();
}

the following summary category gets merrily collected but warning an error:

public summary category abstractthing implements ianything {
  open vacant m1() {}
  open vacant m3() {}
}

can explain why?