use mememto and mediator patterns

v13.0

mediator pattern

use abstract factory and facade patterns

CommandParser now will create CommandValidator and Command objects

use state pattern

v11.0

state pattern

use visitor and iterator patterns

v10.0

iterator pattern

use composite(hierarchy) and flyweight (city) patterns

v9.0

Composite(hierarchy) and flyweight (city) patterns

use bridge and adapter patterns

v8.0

bridge and adapter patterns

user clone and builder patterns

v7.0

clone and builder patterns

use decorator and responsibility chain

v6.0

Decorator and responsibility chain

use proxy and observer patterns

v5.0

proxy and observer patterns

use singleton and interpreter patterns

v4.0

singleton and interpreter