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Doubt in Constructor invocation

 
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From above code, the Output is
Derived value :null
Derived value :derived

But, why the showMethod() of Base class that is Line 1 is NOT invoked?
Please explain the execution flow of the program.
 
Bartender
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Instance variables are initialized after the super constructor returns. But because you invoke an overriden method in the super constructor the method uses variables that aren't initialized yet. That explains the null output.
 
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Your example shows exactly why it's dangerous to call methods that can be overridden from constructors.
 
Abhijit Das
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Hi ,

I am looking for the execution process of the program. Why the showDevice() of the super class, i.e. Base is NOT invoked. My expected output is
base value : base or null

Another doubt, The static variable/ class member is executed at the time of class loading instead of object creation.So, if this is correct, will be called before construct invocation.

Please help me to understand the concept.

FYI, Wouter, the answer is not clearing my doubts. Please go through the question again.
Thnaks
 
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Abhijit Das wrote:Hi ,

I am looking for the execution process of the program. Why the showDevice() of the super class, i.e. Base is NOT invoked. My expected output is
base value : base or null


What is the actual type of the you are creating? The overridden methods are invoked on the actual object.
 
Abhijit Das
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Hi,
According my understanding, the execution steps are as follows.

20 -> 21 -> 16 -> 17 -> 07 -> 08 -> 04 -> 05 -> ...........



Where number represents the line no. shown in the code block.

But, while debug, the execution steps are

20 -> 21 -> 16 -> 17 -> 07 -> 13 -> ->14 -> ....




I think, now it is cleared my question!!!

For Abimaran Kugathasan,

What is the actual type of the you are creating?



- Creating object of the type Derived

The overridden methods are invoked on the actual object.


- Not clear the question
Thanks
 
Abimaran Kugathasan
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In your super class constructor, you've called the instance method. This method is called on the actual object of Derived type. So the the method in the Derived class is invoked.
 
Marshal
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Rob Prime, yesterday, wrote:. . . it's dangerous to call methods that can be overridden from constructors

That's worth repeating.
 
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