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Anno. Class Question

Kay Liew
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Joined: Dec 26, 2003
Posts: 112
Question extracted from MasterExam from KB book.



The answer suggested that "Bing b = new Bing(){"Foo";};" is one of the correct answers. But it does not compile for me. Can someone explain the logic behind this ?

Second, "Bang b = new Bing("Foo"){}; " is wrong because I think it's syntatically incorrect. The suggested answer saying that "incorrect because it violates the rules of polymorphism-you cannot refer to the super class type using a reference variable declared as a subclass type. The super class is not quaranteed to have everything the subclass has. " Especially the last sentence, it completely throw me off. Again, can someone explain the logic for me? Personally, i think it should not even mention about polymorphism at all.

By the way, are the questions in the MasterExam difficulty equivalent to the real exam ?

Thanks in advance,
Kay


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Barry Gaunt
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Joined: Aug 03, 2002
Posts: 7729
Have you checked the errata?

Sorry but I don't know the page that question is on. "Bing b = new Bing(){"Foo";};" is definitely wrong.

Bing b = new Bing("Foo"){}; is OK it means that b is a reference to an object that is an instance of an anonymous class derived from Bing. Notice that the constructor Bing(String s) will be used to construct the new object.

Bang b = new Bing("Foo"){}; is not OK because the new anonymous class is a Bing not a Bang.
[ October 09, 2004: Message edited by: Barry Gaunt ]

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Kay Liew
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Joined: Dec 26, 2003
Posts: 112
Barry,

Thank you for the prompt response. I couldn't "search" any related erata in the URL. The question was came out from the MasterExam CD of Kate and Bates book.

Here is the original question.

Basically the question as, Choose 2 are correctly applicable to the //comment line.


A) Bang b = new Bing("Foo"){};
B) Bing b = new Bing(343){};
C) Bing b = new Bing(){"Foo" ;
D) Bing b = new Bang(){};
E) Bing b = new Bing.Bang("Foo"){};


Which 2 would you choose ? Well, D definitely the right one.

Thanks,
k
Gurpreet Singh
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Joined: Oct 05, 2004
Posts: 34
hey, Kay do you know the reason why

Bing b = new Bing(){"Foo";};

is incorrect. I guess you would have guessed the answer by now.
In case you haven't, "Foo" is not passed to any String variable or
to any variable at all.

Got it.
Kay Liew
Ranch Hand

Joined: Dec 26, 2003
Posts: 112
Gurpreet,

Yeah, I got it now. After i posted this question, I did about 10-13 trials and errors to find out all possible can and can't combination.
Thanks
K
 
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