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Certpal Question on polymorphism

 
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Hi this is a Certpal question that I have compiled and verified but I am having difficulties working out the why?



For this code to compile Best must extend East. My asnwer was East must extend Best (which I confirmed is wrong). The reference variable best points to an object that implements both Best and East. Why doesnt East extends Best work?
 
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The declaration on the right-hand side must be a sub-type of the one declared on the left-hand side. Take, for example, #1. Test56 is a child of Best, therefore in order for it to compile Best needs to extend East.

I hope that helps.
 
shuba gopal
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Aj thanks, this really helped
 
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if you are going to cast(up/down) between two type you must maintain relationship between them otherwise it leads to incompatible types.
 
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Consider East extends Best

So in your example


Here you are assigning a parent to child so you have to downcast it.Like this :

If it was Best extends East

Here Upcasting is done automatically by the compiler.
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