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child object and parent object... assignable?

Akhilesh Trivedi
Ranch Hand

Joined: Jun 22, 2005
Posts: 1511
Let us say, class A that extends class B and their respective objects are "a" and "b"...

A= child class
B= parent class
Now, which one is valid to assign.

a=b; or
b=a;
or both?


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Kedar Dravid
Ranch Hand

Joined: May 28, 2004
Posts: 333
Valid: b=a
Invalid: a=b
Shubhada Nandarshi
Ranch Hand

Joined: Jun 10, 2005
Posts: 59
A= child class
B= parent class

then
b=a; is valid implicitly

But you can do:
a=(A)b; explicitly. This may result in runtime exception.
(ClassCastException).For that u can use try catch block.


bye

Shubha.


Shubhada
reubin haz
Ranch Hand

Joined: May 12, 2005
Posts: 287
Originally posted by Shubha AN:
A= child class
B= parent class

then
b=a; is valid implicitly

But you can do:
a=(A)b; explicitly. This may result in runtime exception.


I think it alway result in runtime exception. Can someone judge me this please?


SCJA, SCJP5.0, SCBCD, SCWCD
Sangita Mishra
Greenhorn

Joined: Jun 15, 2005
Posts: 22
No in certain cases (when assigning child object to Parent reference), it gives runtime expetion. see example below:
 
It is sorta covered in the JavaRanch Style Guide.
 
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