当你做一个ArrayList不指定对象类型，它自动创建它，当你添加的第一个对象？ [英] When you make an ArrayList without specifying the object type, does it create it automatically when you add the first object?

问题描述

例如，而不是做

ArrayList<ClassName> variableName;

您

ArrayList variableName;

然后再添加类型的对象类名

then later you add an object of type "ClassName"

variableName.add(objectName);

会自动设置你的阵列的类型为

will that automatically set the type of your array as

ArrayList<ClassName>

推荐答案

没有。泛型仅用于编译时。你只是失去了检查的好处。在运行时，所有的通用信息将被删除

No. Generics are for compile time only. You are just losing the benefit of that check. At runtime all generic information is erased

在换句话说，

ArrayList<Type> 

在运行时只是一个ArrayList。这样做，经过短短一个List的好处是，当你写你的code，编译器会检查你不把任何东西不合适在列表中。

at runtime is just an ArrayList. The benefit of doing that over just a List is that when you are writing your code, the compiler will check that you dont put anything inappropriate in your list.

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