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Adapter vs Facade vs Proxy - Structural Pattern Comparison

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Solution Trace

▶

Steps

setup

Create PaymentGateway instance

We instantiate the PaymentGateway class which provides the make_payment method to process payments.

💡 This class represents the existing interface that clients want to use but may not be compatible with their expected interface.

Line:gateway = PaymentGateway()

💡 Understanding the original class's interface is essential before adapting or wrapping it.

class PaymentGateway:
    def make_payment(self, amount):
        print(f"Processing payment of {amount}")  # STEP 1

class PaymentAdapter:
    def __init__(self, gateway):
        self.gateway = gateway  # STEP 2

    def pay(self, amount):
        self.gateway.make_payment(amount)  # STEP 3

class LightingSystem:
    def turn_on(self):
        print("Lights on")  # STEP 4
    def turn_off(self):
        print("Lights off")  # STEP 6

class SecuritySystem:
    def arm(self):
        print("Security armed")  # STEP 6
    def disarm(self):
        print("Security disarmed")  # STEP 7

class HomeFacade:
    def __init__(self, lighting, security):
        self.lighting = lighting  # STEP 5
        self.security = security  # STEP 5

    def leave_home(self):
        self.lighting.turn_off()  # STEP 6
        self.security.arm()       # STEP 6

    def arrive_home(self):
        self.security.disarm()    # STEP 7
        self.lighting.turn_on()   # STEP 7

class Database:
    def query(self):
        print("Querying database")  # STEP 7

class DatabaseProxy:
    def __init__(self, db):
        self.db = db  # STEP 8
        self.authenticated = False  # STEP 8

    def authenticate(self, user):
        if user == "admin":  # STEP 9
            self.authenticated = True
            print("User authenticated")
        else:
            print("Authentication failed")

    def query(self):
        if self.authenticated:  # STEP 10
            print("Proxy: Access granted")
            self.db.query()  # STEP 10
        else:
            print("Proxy: Access denied")

# Usage
# Adapter
gateway = PaymentGateway()  # STEP 1
adapter = PaymentAdapter(gateway)  # STEP 2
adapter.pay(100)  # STEP 3

# Facade
lighting = LightingSystem()  # STEP 4
security = SecuritySystem()  # STEP 4
home = HomeFacade(lighting, security)  # STEP 5
home.leave_home()  # STEP 6

# Proxy
db = Database()  # STEP 7
proxy = DatabaseProxy(db)  # STEP 8
proxy.authenticate('admin')  # STEP 9
proxy.query()  # STEP 10

📊

Adapter vs Facade vs Proxy - Structural Pattern Comparison - Watch the Algorithm Execute, Step by Step

Watching each pattern's mechanism unfold visually helps you grasp their distinct roles and how they simplify or control interactions in complex systems.

Step 1/10

·Active fill★Answer cell

Setup of the adaptee class which the Adapter will wrap.

PaymentGateway

+make_payment(amount)()

Practice

(1/5)

1. In the object-oriented design of a Snake and Ladder game, which component is primarily responsible for managing the state transitions of a player's position after a dice roll?

easy

A. The Dice class, since it generates the number that determines movement

B. The Player class, as it holds the current position and updates it directly

C. The Board class, because it contains the snakes and ladders and applies their effects

D. The GameController class, which orchestrates the game flow and updates player positions accordingly

5. Consider the following buggy code snippet from a thread-safe observer pattern implementation. Which line contains the subtle bug that can cause unsubscribed observers to still receive notifications?

def unsubscribe(self, observer, event_type):
    with self.lock:
        if event_type in self.observers:
            self.observers[event_type].remove(observer)
            if not self.observers[event_type]:
                del self.observers[event_type]

Assume that observer may not be subscribed to event_type when unsubscribe is called.

medium

A. Line 5: No handling of empty observer dictionary

B. Line 2: Lock is not acquired properly

C. Line 3: Missing check if observer is in the set before remove()

D. Line 4: Deleting event_type key prematurely

Recommended

Ready to prove it?

Pass the test and this pattern moves unknown strong while earning +1 Grip toward your certificate.

10 questions~5 mineasy hard

Create PaymentGateway instance

Create PaymentAdapter wrapping PaymentGateway

Adapter translates pay() to make_payment()

Create LightingSystem and SecuritySystem instances

Create HomeFacade instance with subsystems

Call leave_home() on HomeFacade

Create Database instance

Create DatabaseProxy wrapping Database

Authenticate user with DatabaseProxy

Proxy forwards query() call to Database

Key Takeaways

Practice

Solution

Step 1: Understand the role of Dice

Step 2: Consider Player class responsibilities

Step 3: Analyze Board class role

Step 4: Role of GameController

Final Answer:

Quick Check:

Solution

Step 1: Understand the requirement for families of related objects

Step 2: Match pattern to requirement

Final Answer:

Quick Check:

Solution

Step 1: Understand Singleton purpose

Step 2: Identify trade-offs

Step 3: Address misconceptions

Final Answer:

Quick Check:

Solution

Step 1: Understand strict LSP enforcement

Step 2: Analyze trade-offs

Step 3: Evaluate options

Final Answer:

Quick Check:

Solution

Step 1: Analyze unsubscribe logic

Step 2: Identify fix

Final Answer:

Quick Check:

Ready to prove it?