类级别注释与接口 [英] class level annotations vs interfaces

问题描述

我正在查看一些代码，其中使用类级别注释将属性添加"到某些类，稍后使用反射访问和使用这些属性.

I am looking at some code where class level annotations are used to 'add' properties to certain classes, later using reflection these properties are accessed and used.

我的问题:什么时候使用注解向类添加新字段而不是使用接口是合适的.这有什么优点和缺点?

My question: When is it appropriate to use an annotation to add new fields to a class, instead of using an interface. What are some benefits and drawbacks to this?

推荐答案

我不知道注解会取代界面，但我能看出它的魅力.不过，这一切都取决于实现.

I don't know that annotations would ever replace an interface, but I can kind of see the allure. It all depends on the implementations though.

注解提供元数据来进一步描述代码，消费者(大部分时间)使用反射在运行时解释这些代码.使用接口，这个实现契约被明确定义.

Annotations provide meta data to further describe code, which a consumer (most of the time) interprets at runtime using reflections. Using an interface, this contract of implementation is clearly defined.

你可以:

interface CrudDao<T> {
   Serializable create(T t);
   T read(Serializable id);
   void update(T t);
   void delete(T t);
}

这将是一个繁琐的合同，并且可能会导致某种方法链.

This would be a cumbersome contract to implement, and would likely incur some sort of method chaining.

相反，您可以执行以下操作:

Instead you could do something like:

class SomeDao {

   @Create
   long create(SomeEntity e) { // code }

   @Read
   SomeEntity read(long id) { // code }

   @Update
   void update(SomeEntity e) { // code }

   @Delete
   void delete(SomeEntity e) { // code }
}

缺点是使用起来比较麻烦:

The drawback is that it would be cumbersome to use:

class CrudFactory {
    long create(Class clazz, Object obj) {
       // loop through methods
       // find method with @Create
       // call method
    }    
}

这个例子中的注释在大多数情况下都是多余的，IMO.关于定义明确、文件齐全的合同，有些话要说.

Annotations in this example would be overkill a majority of the time, IMO. There is something to be said about a clearly defined, well documented contract.

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