Re: an inheritance question

From:

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Newsgroups:

comp.lang.java.programmer

Date:

Wed, 23 May 2007 10:36:54 -0400

Message-ID:

<f31ji7$8sa$1@news.nems.noaa.gov>

Ingo R. Homann wrote:

It depends:

(a) doA() only makes sense on Objects of type ChildA. Then use a proper
declaration:
ChildA person=new ChildA();
person.doA();

It is this case. But, I hope to have Base class hold the reference
_person. Because:

public Base {
     protected Person _person;
     ...
}

public Sub extends Base {
     _person = new ChildA();

     _person.doA(); //WRONG !!!! error message: doA() is unresolved

}

public Sub2 extends Base {
     _person = new ChildB();

     _person.doB(); //also wrong!!!

}

Otherwise, I would just:

public Sub {
    ChildA person = new ChildA();

    person.doA();
}

public Sub2 {
    ChildB person = new ChildB();

    person.doB();
}

(d) Your whole design is broken. Then a quick and dirty solution would
be to do "
> Some

type casting to force _person as ChildA ?

Could you give me more information? My boss gave this layout. I think he
wants me to do downcasting. I googled, but didn't find much direct example.

Thank you.