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Java - deadly diamond of death pblm
Expert: Beenish - 11/3/2009
Question
hello
I am learning java nw.I saw that java doesn't allow multiple inheritance because of this pblm. As a solution they are providing interfaces where the functions are abstract ( so who ever is implementing must write the function).
I still don't get how they have got rid of the deadly diamond of death pblm? It would be nice if you can explain with an example. 'A' is the super class 'B' and 'C' inherit from 'A' , then 'D' is inheriting from 'B' and 'C'. So this causes daimond pblm.So how you solve this using interface?
Answer
Hello,
Thankyou for your question.
Well, first you should completely understand what is the deadly diamond of death.
Lets say, if Java would have supported multiple inheritance which means inheriting
from one or more class. Lets say we had a class A which had some method doStuff().
Then lets say there were two classes B and C which extended from A. Both will inherit
method doStuff() and they both will provide their own implementation means overriding
the functionality provided by the super class. Now lets say if Java would have supported
multiple inheritance and another class D would have come into picture and it extended
from both class B and C, now at this point where the deadly diamond of death will occur.
Class D will be confused which implementation should i really inherit. Class B or C?
This kind of situation gets avoided by interfaces because interfaces are only contracts,
and they don't provide you with implementations. It is upto the classes to provide the
implementations which implement them. So such kind of version conflict will never occur
in case of interfaces as there are no implementation details provided just the signature.
No two implementations can ever conflict as in case of situation i described above.
Now lets say, if you have the following scenario
interface B{
void eat();
}
interface A{
void eat();
}
public class C implements B,A{
public void eat() {
// TODO Auto-generated method stub
}
}
In this case only one eat() method will exist in class C because duplicate methods
are not allowed. Does this make sense to you now?
Hope this helps,
Ben
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