What is swim lane for an activity diagram what are swimlanes

What is swim lane for an activity diagram? what are swimlanes used for? must we use swim lanes (yes or no)?
Is encapsulation the same thing as information hiding? why? or why not?
What is the difference between a superclass and a subclass? how are superclass-subclass relationships represented in the uml

Solution

Swim lane are used in activity diagram to distinguish the activity diagram visually on the basis of certain role or responsiblities like if we talk about a store then it could be divided on the basis of role like Customer,Salesman,Cashier etc. These lines could be drawn vertically or horizontally.

Superclass by definition is the class which is inherited by any other class and that class will take all the features of superclass and can reuse those. Subclass is the class which inherits the superclass, it will have the features of super class plus it can have its additional features and attributes.