how can this downcast works:(B)super.clone()?

Question

class A { 

}
public class B extends A {

public static void main(String[] args) {
     A m = new A();
     B n = (B)m;
}
}

this code can not be complied. However, in the code below, this downcast works.

 class A { 

}
public class B extends A implements Cloneable{

@Override
public B clone() throws CloneNotSupportedException {
return (B)super.clone();
}
public static void main(String[] args) {
     B m = new B();
     B n = m.clone();
}
}

so, why this downcast works?

=============Correction============================

sorry for my fault, it should be B n = **(B)**m;, not B n = m;. I'm very sorry. I have corrected it in the above code.

In second case there is no downcast, Assuming the Test should replace with B, Other wise it's a compilation error. — Krushna, Aug 07 '13 at 06:15
thanks to @RohitJain, and sorry for Joachim and Krushna. I have realize waht my fault is and correct in the question. — andy, Aug 07 '13 at 08:42

score 1 · Accepted Answer · answered Aug 07 '13 at 06:11

1

Even in first case -; class A {

       }
    public class B extends A {

    public static void main(String[] args) {
     A m = new A();
   //  B n = m;
     B n = (B)m;
   }  
     }

It's work.

answered Aug 07 '13 at 06:11

Mohsin Shaikh

494
1
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11

3

Well, it _compiles_. Works is another matter. – Joachim Isaksson Aug 07 '13 at 06:15
Yes it work - or rather IDE says it will work, because you type casted it, but you will still get runtime error. – Antoniossss Aug 07 '13 at 06:15

score 0 · Answer 2 · answered Aug 07 '13 at 06:14

0

WHAT? You cannot cast A to B no mather what you people are saying IF A extends B than B can be threated as insance of A and B but A cannot be instance of B.

answered Aug 07 '13 at 06:14

Antoniossss

31,590
6
57
99

how can this downcast works:(B)super.clone()?

2 Answers2