java - What type returns the get method? -

if type variable wildcard, return type of method be?

public class myclass{ }  list<? extends myclass> nms = new arraylist<myclass>(); nms.add(new myclass()); //compilation error myclass n = nms.get(0); //compiles fine 

the thing return type of get not pure myclass type. eclipse's telling me it's cap#2 , argument of add method cap#1 cap#2 subtypeof myclass, myclass not subtypeof cap#1?

so, i'm interested compiler captured type in class hierarchy? if create

public class mysubclass extends myclass{ } 

will cap#2 subtype of mysubclass either?

no, <? extends myclass> unknown class extends myclass (can myclass itself). there no guarantee has relationship mysubclass.

replace myclass number , mysubclass bigdecimal. have <? extends number>. long. long has nothing bigdecimal (even though both extend number).

as 2 methods, get return myclass. add accept instances of unknown type (and since compiler cannot enforce unknown types, won't let add except null).