null a valid subtype of object ?

[ali kamran]

Given this code snippet, what can be inserted in the fragment ?

class Marmaduke
{}
public class Cert extends Marmaduke 
{
    public static void main(String [] args)
    {}
    public Marmaduke go()
    {
        // Insert code fragment here
    }
}

this is from certpal
can somebody please explain why null is valid code fragment

[saloni jhanwar]

Code tag and source of post please.

[Seetharaman Venkatasamy]

ali kamran wrote:can somebody please explain why null is valid code fragment

null is an valid return type in this regard. by the way: what are the other options?

[ali kamran]

Seetharaman Venkatasamy wrote:

ali kamran wrote:can somebody please explain why null is valid code fragment

null is an valid return type in this regard. by the way: what are the other options?

May you please elaborate "in this regards" ?.The correct answers is 2,3 and 4.The return type is of the same class or a sub class.how is this and null subtype ?


Options

1.) return new Object();

2.) return this;

3.) return new Marmaduke();

4.) return null;

5.) return "";

[Seetharaman Venkatasamy]

*return null* is not only the option then....

[ali kamran]

Seetharaman Venkatasamy wrote:*return null* is not only the option then....

May you please explain how return null is valid.Thank you

[saloni jhanwar]

Marmaduke obj=null;
return obj;

or

return null;

for instance :

int getInt(){
      int i=0;
      return i;
      or
      return 0; 
}

null is not a subtype of object.It is a value that is nothing.

[gurpeet singh]

Return types go through assignment-conversions(for more information refer JLS http://docs.oracle.com/javase/specs/jls/se7/html/jls-5.html#jls-5.2) .

basically it says in assignment conversions, the type of expression must be converted to the type of the variable. also if you look in the return type section in JLS , you will see that they use assignment conversion. so whatever you return must be assignable to the return type mentioned in your method using assignment conversion rules/contexts given in the book. since null can be assigned to any object reference variable, null is a valid return type from any method returning any object.