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Question on Whizlabs Test Question

 
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The following is from a Whizlabs Diagnostic Exam

Just to focus on the problem, the official answer given says that there is
no ClassCastException at runtime.

I would think that there is and I'll explain why I think so.
Line1 (ArrayList b = a) is taking an ArrayList<Circle> and assigning it
to an ArrayList raw reference. That I can live with.
The next line casts b to an ArrayList<Rectangle> and puts it into c, an ArrayList<Rectangle> reference. So I have taken what is actually an
ArrayList<Circle> and stuffed it into an ArrayList<Rectangle> reference by
casting it. Fine! I can see that would get through the compiler but, at
runtime, I would think that the JVM would realize that the true type of b is an ArrayList<Circle> and throw a ClassCastException.

Okay..... what am I missing?



[ September 05, 2008: Message edited by: Bob Ruth ]
 
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when you write ArrayList<Circle> the compiler will remove the <Circle> from this statement. This is called type erasure. So actually the JVM doesn't know that you are assigning ArrayList<Circle> to ArrayList<Rectangle>. for the JVM they are just ArrayList. that's it, the JVM doesn't know about the type of the ArrayLists.
 
Bob Ruth
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That's right. I forgot about Type Erasure having that effect. Thanks for reminding me!
 
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