Dan's Reference Conversion Doubt

[Jas Oberai]

Hi Friends,
This question is from Dan's Questionaire,i am not able to understand the
wordings,can you please tell me what the author means to convey here,and
how can the error be removed from this code.Thanks.

interface I1 {}  interface I2 {}
class Base implements I1 {}
class Sub extends Base implements I2 {}
class Silver {
  public static void main(String []args) {
    Base[] base = {new Base()};
    Sub sub[] = new Sub[1];    // 1
    Object obj = base;         // 2
    sub = (Sub[])obj;          // 3
    I1 []i1 = (I1[])obj;       // 4
}}
 
A:  Run-time error at line 3 
Explanation:
Base is the superclass of type Sub, so a reference to an actual instance
of type Base can not be cast to type Sub. Therefore, a reference to an
array instance of type Base[] can not be cast to type Sub[]. The type of
the reference, obj, is Object. Type Sub[] is a subclass of Object. The
compiler accepts the cast, because the actual instance referenced at run-
time might be of type Sub[]. In this case, the actual type of the instance
referenced by obj at run-time is found to be type Base[], so the result is 
a run-time error. 

[ May 12, 2005: Message edited by: jas oberai ]

[Rohan Kayan]

interface I1 {}
interface I2 {}
class Base implements I1 {}
class Sub extends Base implements I2 {}
class Silver
{
public static void main(String []args)
{
Base[] base = {new Base()};
Sub sub[] = new Sub[1]; // 1
Object obj = base; // 2
sub = (Sub[])obj; // 3
I1 []i1 = (I1[])obj; // 4
}
}

Actually at the compile time it will allow , as we are implicit downcasting.
But at the run time it will check for the actual object in this case the actual object refered by obj is of Base type that's why it will give error . To remove the change

Object obj = sub; // 2

[Timmy Marks]

Simple explaination:

All Women are People, so if you have a Woman you know she is a Person

but

All People are not Women, so if you have a Person you cannot "cast" is as a Woman

now substitute Base for People and Sub for Women and you can see why it is a mistake.