Facade Design Pattern
Introduction
The Facade design pattern is a structural design pattern that provides a smoother interface to a complex system of classes, libraries, or frameworks. It is also referred to as the wrapper pattern. The pattern encapsulates a collection of objects and provides them with a unified interface.
In a nutshell, the Facade pattern creates a single, simplified interface to a complex system. It protects clients from the system’s complexity and makes it easier to use.
Example
For example, we can turn on a computer by simply pressing a button, but this involves numerous procedures and operations (e.g. loading programmes from disc to memory etc). In this case, the button acts as a unified interface to all of the underlying procedures for turning on a computer.
# Complex computer parts
class CPU:
"""
Simple CPU representation.
"""
def freeze(self):
print("Freezing processor.")
def jump(self, position):
print("Jumping to:", position)
def execute(self):
print("Executing.")
class Memory:
"""
Simple memory representation.
"""
def load(self, position, data):
print("Loading from {0} data: '{1}'.".format(position, data))
class SolidStateDrive:
"""
Simple solid state drive representation.
"""
def read(self, lba, size):
return "Some data from sector {0} with size {1}".format(lba, size)
class ComputerFacade:
"""
Represents a facade for various computer parts.
"""
def __init__(self):
self.cpu = CPU()
self.memory = Memory()
self.ssd = SolidStateDrive()
def start(self):
self.cpu.freeze()
self.memory.load("0x00", self.ssd.read("100", "1024"))
self.cpu.jump("0x00")
self.cpu.execute()
def main():
"""
main function
"""
computer_facade = ComputerFacade()
computer_facade.start()
>>> main()
Freezing processor.
Loading from 0x00 data: 'Some data from sector 100 with size 1024'.
Jumping to: 0x00
Executing.