title: Spring setter injection not mandatory
body: <p>I read that There is no guarantee in a setter injection that the dependency will be injected as opposed to constructor injection that the dependency is mandatory. </p>
  
  <p>I really don't understand that point. If I write the following method:</p>
  
  <pre><code>@Autowired
  public void setMyBean(MyBean otherBean){
      this.otherBean = otherBean;
  }
  </code></pre>
  
  <p>what does it mean that otherBean won't be injected?</p>