Class ... implements ...

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Hi,

I'm given the following program snippet:

==
class C1
{
 public int n;
}

interface I1
{
 int f();
}

class C2 extends C1 implements I1
{
 public int f()
 {
  n = 18;
 }
}
==
I need to say if the following expressions are valid or not
(justifications are trivial once I'm sure of the answer):

1. C1 obj_1 = new C2();
2. C2 obj_2 = new C1();
3. I1 obj_3 = new C2();
4. I1 obj_4 = new I1();
5. C2 obj_5 = new I1();

I've found that 1. and 3. are valid, when the others (2., 4. and 5.)
are invalid. Am I right?

Thanks.
- --
Merciadri Luca
See http://www.student.montefiore.ulg.ac.be/~merciadri/
- --

Don't try to teach a pig to sing. It doesn't work, and you'll annoy
  the pig.
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