Listvs. ArrayList(1) List? myList new ArrayList?()(2) ArrayList? myList new ArrayList?
List vs. ArrayList
(1) List<?> myList = new ArrayList<?>();
(2) ArrayList<?> myList = new ArrayList<?>();
use (2) if code is the "owner" of the list. This is for example true for local-only variables. There is no reason to use the abstract type List instead of ArrayList. Another example to demonstrate ownership:
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我比较常用的是List<String> creditCardYears = new ArrayList<String>();
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List<T> XXX = new ArrayList<T>();
List是一个接口吧，而arraylits是实现了这个接口的一个类
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区别在于是不是需要使用ArrayList独有的方法