I don’t think there is a way to do that out-of-the-box. A possibly cleaner solution would be:
Stream.of(objects)
.filter(c -> c instanceof Client)
.map(c -> (Client) c)
.map(Client::getID)
.forEach(System.out::println);
or, as suggested in the comments, you could use the cast
method – the former may be easier to read though:
Stream.of(objects)
.filter(Client.class::isInstance)
.map(Client.class::cast)
.map(Client::getID)
.forEach(System.out::println);