Assignments

[Edisandro Bessa]

Given :

interface I1{}
class C1 {}
class C2 extends C1{}
class C3 extends C1{}
class C4 implements I1{}
class C5{}

and the following declarations and assignments :

I1 i1;
C1 c1 = new C1();
C2 c2 = new C2();
C3 c3 = new C3();
C4 c4 = new C4();
C5 c5 = new C5();
 
c1 = c2;      [B]//Legal[/B]
c2 = (C2)c1;  [B]//Legal[/B]
c1 = c3;      [B]//Legal[/B]
c3 = (C3)c1;  [B]//Legal[/B]
i1 = c4;      [B]//Legal[/B]
c4 = (C4)i1;  [B]//Legal[/B]
 
c2 = c3;      [B]//Illegal. Both classes are siblings[/B]
c3 = c2;      [B]//Illegal. Both classes are siblings[/B]
 
c4 = c3;      [B]//Illegal. Classes are not in the same hierarchy[/B]
c3 = c4;      [B]//Illegal. Classes are not in the same hierarchy[/B]
 
i1 = c4;      [B]//Legal. Class implements interface[/B]
c4 = (C4)i1;  [B]//Legal. Class implements interface[/B]
 
c5 = (C5)i1;  [B]//Still legal. Why ??? Class C5 doesn't implement I1[/B]
i1 = (I1)c5;  [B]//Still legal. Why ??? Class C5 doesn't implement I1[/B]

Any comments about the last two sentences would be highly appreciated.

Thanks.

[Changchun Wang]

you will find the answer from this url

the complier infer the subclass of c5 maybe implements il interface
so it will compile well,but generate a runtime time error

[ March 31, 2006: Message edited by: Changchun Wang ]

[Edisandro Bessa]

Thank you Changchun,

Very good link. Thanks.