Array Object and Ordinary object Initialization

Question

I have 3 objects root1,root2,root3 where they are present in root[] (Array Object) which is a collection of objects.

I have initialized the

Answer 1

I have 3 objects root1,root2,root3

No you don't. You have three variables, and they are all null.

where they are present in root[]

Nothing is present in root[] except three nulls when you initialize it.

I have initialized the Node class using root[0]

You have instantiated the Node class, and stored the reference into root[0].

// It is printing null value.

With this code it should be throwing NullPointerException.

root[0]=root1

No it doesn't. You overwrote it in your loop, and in any case when you did the (pointless) array initialization, root1 was null, as you didn't initialize it.