Bộ sưu tập, bạn cũng thực hiện iterator (), và chỉ thực hiện iterator () một mình đòi hỏi nỗ lực chỉ hơi ít hơn so với kế thừa từ AbstractCoUection. Tuy nhiên, nếu lớp học của bạn đã được thừa kế từ một lớp khác, sau đó bạn có thể không còn kế thừa từ AbstractCollection. | Simpo PDF Merge and Split Unregistered Version - http A dynamic instanceof The method provides a way to dynamically test the type of an object. Thus all those tedious instanceof statements can be removed from typeinfo Using isInstance import . import . import . import static . public class PetCount3 static class PetCounter extends LinkedHashMap Class extends Pet Integer public PetCounter super 0 public void count Pet pet eliminates instanceofs for Class extends Pet Integer pair entrySet if .isInstance pet put 1 . . . . public String toString StringBuilder result new StringBuilder for Class extends Pet Integer pair entrySet .getSimpleName -2 return public static void main String args PetCounter petCount new PetCounter for Pet pet 20 printnb .getSimpleName pet print print petCount . . Output Rat Manx Cymric Mutt Pug Cymric Pug Manx Cymric Rat EgyptianMau Hamster EgyptianMau Mutt Mutt Cymric Mouse Pug Mouse Cymric Pet 20 Dog 6 Cat 9 Rodent 5 Mutt 3 Pug 3 EgyptianMau 2 Manx 7 Cymric 5 Rat 2 Mouse 2 Hamster 1 In order to count all the different types of Pet the PetCounter Map is preloaded with the types from . This uses the class which takes an Iterable the allTypes List and a constant value zero in this case and fills the Map with keys taken from allTypes and values of zero . Without pre-loading the Map you would only end up counting the types that are randomly generated and not the base types like Pet and Cat. Type Information 411 Simpo PDF Merge and Split Unregistered Version - http .
