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April 2001



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oops property...

Posted by G.Salai Sivamal on June 04, 2001 at 7:05 AM

> hi
> i made a class like this
> class a extends Object implements Runnable
> {
> public static void main(String s[])
> {
> a a1=new a();
> Object o=a1;
> Runnable r=o;
> }}
> however this does not compiler as it asks for a explicit cast
> however changing the program as
> Runnable r=a1;
> Object o=r;
> does not require any cast .please explain why.
> gopal

You cannot do downcasting in java. Means, you cannot assign a parent object to child object without doing explicit casting.
thats why you getting error..

since Object is the root of all the jdk classes. the Runnble was inherited from the Object some it is not compilling.

do it like, it will compile
Runnable r=(Runnable)o;

Salai Sivamal.G


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