Difference between object creation and assignment of Parent Class and Child Class

C c=new C() P p=new C()
If we know exact runtime type of object then we should use these approach If we do not know exact runtime type of object then we should use these approach(polymorphism)
By using child reference we can call both parent and child class method By using parent reference we can call only methods available in parent class and child specific methods we cant call
We can use child reference to hold only for that particular child class object only We can use parent reference to hold any child class object