Does base class object holds the drived class object?

Question

Below is the code and I want to understand few things:

public class Test {
    public void dosomething( ) {
      Derived2 d2 = new Derived2 () ;
      Base bobject = d2;
      string str = "str" ;
      bobject.Method1( str ); // I want to call Method1 of Derived1 class
    }
  }

  public class Derived2 : Derived1 {
    public void Method1( string s ) {

    }
  }

  public class Derived1 : Base {
    public override void Method1( double d ) {

    }

    public override void Method2( double d ) {

    }
  }

  public abstract class Base {
    public abstract void Method1( double d );
    public abstract void Method2( double d );
  }

I would like to know, what exactly happens when we assign derived class object to base abstract class object. I know instantiating abstract class is not possible. In my case, I am deriving class Derived1 and assigning object of Derived2 class to base abstract class object. Now I want to access the Dervied2 class method Method1 which accept string argument. Somehow, I am unable to access this method. There are multiple classes exist which are derived from base abstract class. I want to keep things generic.

See the difference between overriding and hiding described here: http://stackoverflow.com/questions/856449/overloading-overriding-and-hiding. Your overriding the double methods but the string method is hiding Method1 — Ibasa, Sep 24 '13 at 10:04

Dennis · Accepted Answer · 2013-09-24T10:08:33.757

1

what exactly happens when we assign derived class object to base abstract class object

There's no object assignment in you code, there's variable assignment. After assignment, variable bobject refers to the same object, as d2 does. Object type (and anything in the object state) remains unchanged.

Now I want to access the Dervied2 class method Method1 which accept string argument

You can't do this in your sample without casting bobject to Derived2:

((Derived2)bobject).Method1(str)

I want to keep things generic

Then, you shouldn't try to access members, which are not the part of base class.

edited Sep 24 '13 at 10:08

answered Sep 24 '13 at 10:01

Dennis

37,026
10
82
150

as you mentioned "After assignment, variable bobject refers to the same object, as d2 does. Object type (and anything in the object state) remains unchanged". Then why can not I access Method1 of Derived2? – User1551892 Sep 24 '13 at 10:43
Because the type of *variable* (not the type of *object*, that variable refers!) is `Base`. Since `Base` doesn't contains desired method, you can't access it. – Dennis Sep 24 '13 at 11:07

score 0 · Answer 2 · answered Sep 24 '13 at 10:05

0

bobject is a type of Base which has two methods which accept a double, not a string (That method is defined in Derived2's implementation).

To do what you requrie you'd need to cast bobject to Derived2, like:

var d3 = bobject as Derived2;
d3.Method1("String");

answered Sep 24 '13 at 10:05

Darren

68,902
24
138
144

`bobject = new Derived1(); var d3 = bobject as Derived2; d3.Method1("String");` - happy debugging. – Dennis Sep 24 '13 at 10:10

score 0 · Answer 3 · answered Sep 24 '13 at 10:36

0

You could even do

(bobject as Derived2).Method1(string);

This is because the resolution is based on the variable type.

answered Sep 24 '13 at 10:36

tomkuj

81
1
5

Does base class object holds the drived class object?

3 Answers3