Question

Here I have few Questions:

1)I tried to return a null value from a method,something like this(only when TypeCasted into object) :

 public static Object returns()
{
   return (Object)null ;
}

And stored the Object:

 ...main()..{
 Object obj=  returns();
 ...}

When i checked:

  if( obj.equals(obj))

Threw a NullPointerException

But,

 if(null==null)
 System.out.println("works");

Compiled and gave right output.Any reasons for this?

2) Also, when i tried:

 public static Object returns()
{
  return (Object)void ;
}

Gave me Syntax Error.Any reasons?

3) Can this behaviour be different in C/C++ ?Or any other OO Language?

Answer 1

You can not call equals on null instead you should use ==. Note that calling == and equals is not the same. == compares references while equals is a method which by convention compares values. As the null object has no value this has no meaning for it.

Void is not a value in any language and so it can not be casted to anything(in this case Object).

In C++ to return NULL you will have to return a pointer. To compare the returned object you will have to type something like:

 if( *obj == *obj)

And again this will fail as obj is NULL. In any language I know you will have to do an explicit check for null before comparing.

EDIT: come to think a bit what you try will work in ruby