even if we specify extends to other class.It extends to object class.

I'm not sure what distinction you are trying to make here. A class can only extend one class. That class, in turn, can only extend one class, etc all the way to Object.
Consider

class A {...}
which is exactly the same as
class A extends Object {...}
then
class B extends A {...}
class C extends B {...}
...
class Z extends Y {...}

It would be totally misleading to say "class Z extends Y and Object" without mentioning B..Y