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A Question From TestLab

Neil Muya
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Joined: Oct 26, 2009
Posts: 30
Which of the following statements are true?(Choose three)

This is the box that i should checked.

"Interface "is-a" java.lang.Object"

This was the explanation:
Answer-I is correct, because any object, which has an
interface-reference, can be implicitly casted to
a java.lang.Object reference, without doing any explicit cast.


For what I know an interface does not extend the Object class..

hmmm or maybe i did not get the question right.

Hope you guys can help me with this thank you!
Neha Daga
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Joined: Oct 30, 2009
Posts: 504
I read this in K&B:
In java everything that is not a primitive is an Object.


SCJP 1.6 96%
Devaka Cooray
ExamLab Creator
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Joined: Jul 29, 2008
Posts: 3102
    
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Neil Muya wrote:A Question From TestLab

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Simran Dass
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Joined: Jan 09, 2010
Posts: 183


A small example for the explanation given in the EXAMLAB

java.io.Serializable sb = new String();
Object o = sb;


Hope now you get it
Rohan Kayan
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Joined: Sep 17, 2004
Posts: 123
It is still not clear to me ,



In above example String "is-a" an Object that is why the assignment in second line worked. But how can we say that Interface "IS-A" java.lang.Object ?


SCWCD 1.4, SCJP 1.4
raj malhotra
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Joined: Feb 22, 2007
Posts: 285
Try this:
rushikesh sawant
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Joined: Dec 22, 2009
Posts: 65
All objects implicitly extends java.lang.Object.
Interface defines a set of methods that its implementing classes must implement.
here,



String class IS-A Serializable.
string class' object is-a serializable.
so, a particular object IS-A particular interface.
hence, Interface IS-A Object.

it is a logical IS-A relationship.

SCJP 5.0 100%
Parambir Singh
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Joined: Sep 05, 2004
Posts: 40

If an object of type A can be cast to type B, we can say that 'A is a B'.

E.g. Object o = new String();
Hence, String "is a" Object

Serializable s = new String();
Hence, String "is a" Serializable

And, Object o = s;
Hence Serializable "is a" Object

And in the last statement, s can be an object implementing any interface, therefore Interface "is a" Object is true.


SCJP, SCMAD
Rohan Kayan
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Joined: Sep 17, 2004
Posts: 123
I think this one is a better example to understand that Interfaces are compiled as .class files and every classes are itself an Object in Java , that is why Interfaces "IS-A" java.lang.Object
 
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subject: A Question From TestLab