Question: I want to understand this:

```
ParentClass p=new ChildClass(); 
//Here ChildClass extends ParentClass

```

Is `p` object of `ParentClass` or of `ChildClass`?

Answer: 
Think about `p` as a view on the given object. You can view a `Dog` as an `Animal` (in which case you can e.g `feed()` it), or you can view it as a `Dog` (so you can get it to `bark()`). In other words, the variable's type that references an object will restrict what you can call on it, but does not change the type of the object.
P is a reference in the stack of type ParentClass pointing to a childClass instance in the heap ,this enables you to just call class members defined in ParentClass and take advantage of Polymorphism on runtime through method overriding.