Java List 類型轉換

java的類型轉換讓人忍不住在開始編碼前罵一聲  FUCK!

1  子類轉父類 up

List<SubClass> subs = ...;
List<? extends BaseClass> bases = subs;

2 父類轉子類 down

//強轉
public class TestA {}
public class TestB extends TestA{}

List<TestB> variable = (List<TestB>)(List<?>) collectionOfListA;

3 stream方式

 

collection.stream()
    .filter(obj -> obj instanceof ScheduleIntervalContainer)
    .map(obj -> (ScheduleIntervalContainer) obj)

 

 

 

參考:

1 https://stackoverflow.com/questions/933447/how-do-you-cast-a-list-of-supertypes-to-a-list-of-subtypes

2 https://stackoverflow.com/questions/35743525/java-8-stream-cast-list-items-to-type-of-subclass