Decorator Pattern

Use case: We want to make a pizza with toppings. A pizza can have no toppings which can assume it will be the base pizza (after asking the pizza place owner who wants this feature). 

Use case: We need to create a text filtering system. Given a string we should be able to strip out any html tags or any other malicious code in that string. The consumer of that system could use any or all of the filters available to him.

Use case: We need to calculate the price of a booking agency according to the amenities a customer would select during the checkout process Such amenities are WiFi connection, breakfast and OLED TV station in the room. We should also make available to the customer to view his/her amenities.