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1.4....K$B question

gagan bhatia
Greenhorn

Joined: May 07, 2007
Posts: 2
the foll is a question of chapter 3 Q 2..
1 import java.awt.*;
2 class T extends C{
3 PSVM(String[] args){
4 T t = new T();
5
6 }
7 }
//PS. T is ticker and C is Component..

What could be legally inserted in line 5...??

One of the wrong options are...

F......boolean test = (t instanceof String);

acc to the expn, " string is not in the heirarchy of t object"

My doubt, if this is so, i accept, but still it is legal. the implications of this is test=false. that is it. how come the option is wrong???
it is legal, but false...

please help o'veterans..
John Stone
Ranch Hand

Joined: May 04, 2007
Posts: 332
because compiler can at compile-time tell, that t (Ticker) is not related to String.
Compiler knows that Ticker is not ancestor nor descendant of String, and consider parameters (of instanceof) as incompatible.

try to change t to Object variable


and now it is working. t is of type Object, so it is possible to have String object reference in type Object reference (upcasting).

when t is Ticker, it doesn't look like upcasting, doesn't look like downcasting, and you have compile-time error: incompatible types

> please help o'veterans
:-)
Barry Gaunt
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Joined: Aug 03, 2002
Posts: 7729
Hello "java ojava"-

Welcome to JavaRanch.

On your way in you may have missed that we have a JavaRanch Naming Policy for displayed (screen) names. Your displayed name must consist of a first name (or an initial), a space, and a family name (in that order) and not be obviously fictitious. Since yours "java ojava", does not conform with it, please take a moment to change it, which you can do right here.

Posters with nonconforming displayed names will be locked out of JavaRanch after a few posts using those names.

Thanks
-Barry

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gagan bhatia
Greenhorn

Joined: May 07, 2007
Posts: 2
Orders followed SIR..
Barry Gaunt
Ranch Hand

Joined: Aug 03, 2002
Posts: 7729
Originally posted by gagan bhatia:
Orders followed SIR..


Thankyou.
 
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subject: 1.4....K$B question