anchor.diff:  .alert.is-helpful
     :marked
       ### Take a break!
  +    
       ### 休息一下！
       
       This much Dependency Injection knowledge may be all that many Angular developers
  
positive.code:   The `MinimalLogger` is an abstract class. 
    
    该`MinimalLogger`是一个抽象类。
  +makeExample('cb-dependency-injection/ts/app/date-logger.service.ts','minimal-logger')(format='.')   
  :marked
    We usually inherit from an abstract class.
  
negative.code:   confirms that the `alex` parameter is null.
    *We cannot inject a parent by its base class.*
    
    可惜这样不行。[在线例子](/resources/live-examples/cb-dependency-injection/ts/plnkr.html)确认了`alex`参数是null。
    *我们不能通过基础类注入父级*
    
    <a id="class-interface-parent"></a>
    ### Find a parent by its class-interface
    
    ### 通过类-接口找到一个父级
    
    We can find a parent component with a [class-interface](#class-interface).
  