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Programmer Certification (SCJP/OCPJP)
Joined: Aug 11, 2006
Feb 06, 2007 21:01:00
Upcasting DownCasting example please.
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Joined: Sep 23, 2000
Feb 06, 2007 21:43:00
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Joined: Feb 06, 2007
Feb 08, 2007 12:08:00
a = new
Collection c = a; // upcast implicit no need for (
b = (
)c; // downcast requires explicit cast
upcast dont require an explicit cast as a subclass is always guaranteed to pass the is-a
with its parent. ie
is a Collection.
downcast requires an explicit cast because the object being cast might not be what its being cast to. You are basically saying to the compiler trust me i know what im doing.
It is sorta covered in the
JavaRanch Style Guide
subject: UpCasting DownCasting
widening and casting
downcasting or upcasting of ref variable
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