问题描述
我有一组类，它们都实现了一个具有方法 isValid() 的验证接口.我想将一组对象——所有不同的类——放入一个 ArrayList，循环遍历它们并在每个对象上调用 isValid().
I have a group of classes that all implement a validation interface which has the method isValid(). I want to put a group of objects--all of different classes--into an ArrayList, loop through them and call isValid() on each.
这是我的代码
Email email = new email();
Address address = new Address();
ArrayList<? extends Validation> myValidationObjects = new ArrayList();
但是当我尝试这样做时:
But when I try to do:
myValidationObjects.add(email);
我明白了:
ArrayList 类型中的 add(capture#2-of ? extends Validation) 方法不适用于参数(电子邮件)
Email 和 Address 都实现了验证.
Both Email and Address implement Validation.
根据本文档，我应该能够对接口和子类使用 extends.
According to this document, I should be able to use extends for both interfaces and subclasses.
推荐答案
您可以使用:
List<Validation> myValidationObjects = new ArrayList<>(); // Java 7
List<Validation> myValidationObjects = new ArrayList<Validation>(); // pre Java 7
现在您可以将实现Validation的类的任何实例添加到该列表中.
Now you can add any instance of a class that implements Validation to that list.
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