interface Foo {

    default World getWorld() {
        return func_1234_a();
    }

    default World func_1234_a() {
        throw new IllegalStateException();
    }

}

// works
class TE extends TileEntity implements Foo {

}

// works, too
class SomethingElse implements Foo {

   World getWorld() {
       return world;
   }

}