Khalid question...

[Mohamed Shafi]

class Base {
    int i;
    Base() { add(1); }
    void add(int v) { i += v; }
    void print() { System.out.println(i); }
}
class Extension extends Base {
    Extension() { add(2); }
    void add(int v) { i += v*2; }
}
public class kha5 {
    public static void main(String[] args) {
        bogo(new Extension());
    }
    static void bogo(Base b) {
        b.add(8);
        b.print();
    }
}

options:

1.9
2.18
3.20
4.21
5.22

Ans: 5 -->22.

can anyone explain how???

Shafi.

[ July 25, 2005: Message edited by: Mohamed Shafi ]
[ July 25, 2005: Message edited by: Barry Gaunt ]

[Barry Gaunt]

I'll give you a hint: just follow the basic rules of object construction, bearing in mind that polymorphism is playing a part in the calls to method add in the constructors.

[Rekha Gaikwad]

Hi Mohamed,
I think the progran will work like below.

When u create an object of Extension in bogo method,

1. it will first call constructor of Extension()
2. Which in turn call super() constructor i.e Base constructor
3. Base constructor will call add(1) method. But Acoording to java run time system it will call the method of runtime object which is Extension so it will call add method of Extension which return value of i=2
4.Then control transfer to Extesion class and call add(2) method which leds value i=6
5. After that b.add(8) method will call which will return value i=22.

[Mohamed Shafi]

Thanks Rekha & Barry for your reply.


Regards,

Shafi.

[Prasanta Chinara]

Don't you think its little weired that even before the object is constructed, the polymorphism comes to play ?

The object is still being constructed .. how could the vtable (standard implementation for overriding function) be constructed properly?