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Java Forum / General / October 2006wildcard generics
What is the difference between List<Whatever> and List<? extends Whatever>? > What is the difference between List<Whatever> and List<? extends > Whatever>? You can add an instance of Whatever to a List<Whatever>, but you can't to a List<? extends Whatever>. - Oliver Sounds like it would be useful if Whatever is an abstract class or interface. If you used ArrayList<Whatever> in this case and added an instanace of Whatever to the list and then tried to execute an abstract method you would get a runtime error. By using ArrayList<? extends Whatever> if you tried to do this you would get a compile time error. Cool. > Sounds like it would be useful if Whatever is an abstract class or > interface. If you used ArrayList<Whatever> in this case and added an > instanace of Whatever to the list and then tried to execute an abstract > method you would get a runtime error. By using ArrayList<? extends > Whatever> if you tried to do this you would get a compile time error. > Cool. Note that you can't actually create an instance of an abstract class or interface; you can only create an instance of one of its subclasses. So whenever you invoke an abstract method, it would always resolve to some real, concrete method. - Oliver > What is the difference between List<Whatever> and List<? extends > Whatever>? AFAIK, ListIterator<Whatever> is not compatible with ListIterator<SomethingThatExtendsWhatever>. Regards, Bart. Free MagazinesGet these publications absolutely FREE for up to 12 months. There are no hidden fees and no obligation. Simply choose a title, complete the application form and submit it. Read more ...
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