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Compiler check for interface and class in instanceof case.  RSS feed

 
Greenhorn
Posts: 7
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interface AB{}

class D {}

class C{}

public class InstanceTest
{
public static void main(String[] args)
{
D d = new D();
System.out.println(d instanceof AB);  // returns false;
               System.out.println(d instanceof C); // compilation error due to different types.

}
}

Question: Why for interface, compiler didn't throw error ? There is no relation between Class D and Interface AB.
 
Sheriff
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Utpal Kumar wrote:There is no relation between Class D and Interface AB.



But you don't know that, and neither does the compiler. Consider this class which might be used at some point in time:



So when the compiler sees this:



it's possible that the object d is in fact an instance of type DAB. In which case it would be an instance of type AB.
 
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