## What is an interface?
- An interface is a device or a system that unrelated entities use to interact.
	- A remote control is an interface between you and a television set.

basically the interface has and abstract method which classes have to implement the method to make it 'real'.

Concert realisation of the otherwise abstract method.




## What is a linked list?

- On the linked list every node is an object.
- Has more memory overhead than an ArrayList.
- Each node holds both data and the address of next and previous node.
- It mainly allows efficient *insertion* and *deletion* operations compared to arrays
- Its dynamic, the size of it changes with every change.

# Protected 
prevents the method to be used by anyone but its sub classes.