java 列表与数组列表
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List vs ArrayList
提问by Caner
List<EventHandler<E>> listeners = new List<EventHandler<E>>();
Why the line above fails with:
为什么上面的行失败：
Cannot instantiate the type
List<EventHandler<E>>
无法实例化类型
List<EventHandler<E>>
But this one works:
但是这个有效：
ArrayList<EventHandler<E>> listeners = new ArrayList<EventHandler<E>>();
回答by Bozho
The proper way is:
正确的做法是：
List<EventHandler<E>> listeners = new ArrayList<EventHandler<E>>();
- refer to an object by its interface (
List) - instantiate the object with its concrete type (
ArrayList) (interfaces can't be instantiated)
- 通过接口引用对象 (
List) - 使用其具体类型 (
ArrayList)实例化对象（接口无法实例化）
回答by Markus Lausberg
List is an interface and you can not create an instance of an interface
List 是一个接口，你不能创建一个接口的实例
try
尝试
List<EventHandler<E>> listeners = new ArrayList<EventHandler<E>>();
回答by adatapost
回答by kittylyst
List cannot be instantiated, as it's just an interface.
List 不能被实例化，因为它只是一个接口。
However, you potentially have another problem as well.
但是，您可能还有另一个问题。
Do you really have a class called 'E'? If you do, well, you shouldn't without a very good reason.
你真的有一个叫做'E'的类吗？如果你这样做，那么，你不应该没有很好的理由。
Single letters such as E and T are pretty much exclusively used to denote a generic type parameter. Read it as: "This is a general description of how to make a class or method, without any reference to any specific type - you can parameterize this class by any legal reference type".
E 和 T 等单个字母几乎专门用于表示泛型类型参数。将其阅读为：“这是对如何创建类或方法的一般描述，没有对任何特定类型的任何引用 - 您可以通过任何合法的引用类型来参数化此类”。
So even classes like ArrayList<T>cannot be instantiated - because they are generic "recipes" for classes, not real concrete classes.
所以即使像 ArrayList <T这样的类>也不能被实例化——因为它们是类的通用“配方”，而不是真正的具体类。
回答by Dyonisos
List is only an Interface which is implemented by ArrayList
List 只是一个接口，由 ArrayList 实现
see: http://download.oracle.com/javase/6/docs/api/java/util/List.html
见：http: //download.oracle.com/javase/6/docs/api/java/util/List.html
