使用父级配置或“将父级降级到子级”实例化子对象

Question

I am not sure what the best practice for downcasting from parent to child or creating a B ( extends A ) out of A is.

As an example I have two classes:

The parent one:

public class SoccerPlayer  {

    private String name;
    private SoccerShoe shoe;
    private SoccerJersey jersey;
    /* ... */
}

And the child one:

public class Goalkeeper extends SoccerPlayer {

    private GoalkeeperGlove glove;
    /* ... */
}

---

Now a regular soccer player wants to be a Goalkeeper. What can I do? Obviously the following would not work:

    SoccerPlayerArrayOfTeamA[0] = new SoccerPlayer("Robert");

    /*... new career path ...*/

    SoccerPlayerArray[0] = (Goalkeeper) SoccerPlayerArray[0]

But that is what I would say "I want to do"...
The new Instance of the child class ( Goalkeeper ) should have all variable configurations as the old Instance of the parent class ( SoccerPlayer ). (eg name , jersey ...) Is there an OOP way to do that I do I have to set every variable manually as in the following?

    /*... new career path ...*/

   SoccerPlayer temp = SoccerPlayerArray[0]
   SoccerPlayerArray[0] = new Goalkeeper(temp.getName());
   SoccerPlayerArray[0].setJersey(temp.getJersey());

Answer 1

Checkout Decorator Design Pattern. Eg Java IO classes.

When any object dynamically wants to change its behavior then you can wrap that object with the desired object. Like if C wants to become B then B should have a constructor which accepts C and then the methods in B should use C where ever appropriate. Best example is when FileInputStream wants to become BufferedInputStream you can just create BufferedInputStream by passing FileInputStream in its constructor but it does not need to copy properties of FileInputStream .

Answer 2

向守门员添加一个复制构造函数，该复制构造函数接受SoccerPlayer作为参数。