StackOverflow2013

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plurals

PO
primarykey
Id
18682810
data
AcceptedAnswerId
0
AnswerCount
0
ClosedDate
CommentCount
1
CommunityOwnedDate
CreationDate
2013-09-08T10:47:32.580
FavoriteCount
0
LastActivityDate
2013-09-08T10:47:32.580
LastEditDate
LastEditorUserId
0
OwnerUserId
1798593
ParentId
18682604
PostTypeId
2
Score
1
ViewCount
0
LastEditorDisplayName
text
Body
There are two issues that are getting confused here, the type of a variable or expression, and the class of an object. Each object has a class that is established when it is created through "new" or clone(). That class is fixed for the lifetime of the object. An reference variable or expression is either null or a pointer to some object. The type of a reference variable is indicated by the name of a class or interface. It can only reference a object if the class of the object matches or extends, directly or indirectly, the class, or implements the interface. In effect, the type of the variable guarantees that the object has the corresponding members. <pre><code>A a = new A(); //statement 1 </code></pre> Declares a variable "a" with type A, meaning it can only be null or a pointer to an A, or an object whose class extends A. Initializes it as a pointer to a newly created object of class A. <pre><code>A a1= new B(); //statement 2 </code></pre> Declares a variable "a1" with type A, meaning it can only be null or a pointer to an A, or an object whose class extends A. Initializes it with a pointer to a newly created B. Since B extends A, the conversion of a type B expression to type A is permitted. <pre><code>B b= (B) new A(); // statement 3 </code></pre> The difference here is that A does not extend B. A type A reference can be cast to type B if, and only if, it is null or a pointer to an object of class B, or a class that extends B. Class A does not extend B. The compiler will accept this, because the cast claims that "new A()" is null or refers to a class B object, or an object of a class extending B. It will get a ClassCastException at run time, because that claim is false. The type of a reference variable or expression is determined at compile time. In the course of a program run, it may be null or refer to objects of several different classes, but only class that are appropriate for its declared type.
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Title
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PostAcceptedAnswerId
1. This table or related slice is empty.
PostParentId
1. POWhile creating an object what does left side class indicates and right side class indicates?
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 PostTypePostTypeId
 PTQuestion
PostTypePostTypeId
1. PTAnswer
UserLastEditorUserId
1. This table or related slice is empty.
UserOwnerUserId
1. USPatricia Shanahan
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1. This table or related slice is empty.
PostLinksRelatedPostIdPostId
1. This table or related slice is empty.
PostsAcceptedAnswerId
1. This table or related slice is empty.
PostsParentIdCreationDate
1. This table or related slice is empty.
VotesPostIdCreationDate
1. VO
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 This table or related slice is empty.
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 VTUpMod
CommentsPostId
1. COhi thanks for the information.
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 PO
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 USuser2482323

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