Java 泛型 - 类<接口(interface)>

Question

我创建了一个名为标识符的接口(interface)。实现 Identifier 接口(interface)的类是 MasterEntity bean，如下所示。

public class MasterEntity implements Identifier{

}

在 DAO 方法中，我编写了如下方法签名的方法。

public Identifier getEntity(Class<Identifier> classInstance){

}

现在我想从服务中调用如下方法。

dao.getEntity(MasterEntity.class);

但是我收到编译错误说 -

The method getEntity(Class<Identifiable>) in the type ServiceAccessObject 
is not applicable for the arguments (Class<MasterEntity>)

我知道如果我像下面这样使用它就会起作用。

public Identifier getEntity(Class classInstance){

但是通过指定类型为可识别的Class，如何才能做到呢？

Answer 1

将 DAO 方法签名更改为

public Identifier getEntity(Class<? extends Identifier> classInstance)

通过如上所述声明方法，您指定唯一适用的参数是 Identifier.class本身。能够接受Identifier.class实现，你应该定义 generic type bounds .

List<? extends Shape> is an example of a bounded wildcard. The ? stands for an unknown type, just like the wildcards we saw earlier. However, in this case, we know that this unknown type is in fact a subtype of Shape. (Note: It could be Shape itself, or some subclass; it need not literally extend Shape.) We say that Shape is the upper bound of the wildcard.

您也可以看看这个答案:https://stackoverflow.com/a/897973/1782379