Flyweight pattern - Structural

• reduces the number of objects created and to decrease memory usage and increase performance
• reuses already existing objects by storing them and creates new object when no matching object is found 
• Make instances of classes on the fly to improve performance efficiently, like individual characters or icons on the screen.

Where to use ?

• To reduce the number of objects created, decrease memory footprint and increase performance
• Need to instantiate a large amount of small and fine-grained classes
• To increase runtime cost associated with transferring, finding, or computing extrinsic data 

Implementation example

• Interface Shape implemented by concrete classes : Circle, Rectangle, Square
• A Factory class maintaining a HashMap of keys and different type of Shape objects
• A factory method checking for object presence in map and return it, if exists
• otherwise, create new object and put in the map