将注释值设置为 Class<?> 时出错从一个常数，为什么?

这是我的注释:

@Target( { ElementType.METHOD } )
@Retention(RetentionPolicy.RUNTIME)
public @interface AuditUpdate
{
    Class<?> value();
}

这样就可以了:

@AuditUpdate(User.class)
void someMethod(){}

但是通过这种方式:

private static final Class<?> ENTITY_CLASS = User.class;
@AuditUpdate(ENTITY_CLASS)
void someMethod(){}

我有这个编译错误:

The value for annotation attribute AuditUpdate.value must be a class literal

为什么?这是什么意思?

Why? What does that mean?

谢谢.

推荐答案

这意味着你必须传递一个类字面量，而不是一个变量(即使是常量).

It means that you must pass a class literal, rather than a variable (even if constant).

类文字在 JLS:

15.8.2 类文字

类字面量是由类名组成的表达式，接口、数组或原始类型，后跟."和令牌班级.类文字的类型是 Class.它评估为类由定义定义的命名类型(或 void)的对象当前实例的类的类加载器.

A class literal is an expression consisting of the name of a class, interface, array, or primitive type followed by a `.' and the token class. The type of a class literal is Class. It evaluates to the Class object for the named type (or for void) as defined by the defining class loader of the class of the current instance.

所以，你不能那样做.