Why structural patterns organize class relationships in LLD - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define a structural pattern that connects classes.

LLD

class Adapter:
    def __init__(self, adaptee):
        self.adaptee = adaptee

    def request(self):
        return self.adaptee.[1]()

Drag options to blanks, or click blank then click option'

Aunrelated_method

Bgeneral_request

Cspecific_request

Dundefined_method

Attempts:

3 left

💡 Hint

Common Mistakes

Using a method name that does not exist in the adaptee.

The Adapter pattern wraps an adaptee's specific method to match the expected interface.

2fill in blank

medium

Complete the code to show how a decorator adds behavior to a class.

LLD

class Component:
    def operation(self):
        return "Component operation"

class Decorator(Component):
    def __init__(self, component):
        self.component = component

    def operation(self):
        return self.component.operation() + [1]

Drag options to blanks, or click blank then click option'

A" with added behavior"

Bself.component.operation()

C" base behavior"

Dself.operation()

Attempts:

3 left

💡 Hint

Common Mistakes

Calling self.operation() recursively causing infinite loop.

The decorator extends the original operation by adding extra behavior as a string.

3fill in blank

hard

Fix the error in the composite pattern code to correctly add child components.

LLD

class Composite:
    def __init__(self):
        self.children = []

    def add(self, component):
        self.children.[1](component)

Drag options to blanks, or click blank then click option'

Aadd

Bappend

Cinsert

Dextend

Attempts:

3 left

💡 Hint

Common Mistakes

Using add which is not a list method in Python.

To add a single component to the children list, use the append method.

4fill in blank

hard

Fill both blanks to complete the proxy pattern that controls access to a resource.

LLD

class Proxy:
    def __init__(self, real_subject):
        self.real_subject = real_subject

    def request(self):
        if self.check_access():
            return self.real_subject.[1]()
        else:
            return [2]

Drag options to blanks, or click blank then click option'

Arequest

B"Access denied"

CNone

Dcheck_access

Attempts:

3 left

💡 Hint

Common Mistakes

Returning None instead of an access denied message.

The proxy calls the real subject's request method if access is allowed; otherwise, it returns an access denied message.

5fill in blank

hard

Fill all three blanks to complete the flyweight pattern that shares objects efficiently.

LLD

class FlyweightFactory:
    def __init__(self):
        self._flyweights = {}

    def get_flyweight(self, key):
        if key not in self._flyweights:
            self._flyweights[[1]] = Flyweight([2])
        return self._flyweights[[3]]

Drag options to blanks, or click blank then click option'

Akey

C"new_key"

DFlyweight

Attempts:

3 left

💡 Hint

Common Mistakes

Using different keys for storing and retrieving flyweights.

The factory uses the key to check and store flyweight objects, ensuring reuse.

Practice

1. What is the main purpose of structural design patterns in organizing class relationships?

easy

A. To simplify system design by organizing how classes relate

B. To improve the speed of the program execution

C. To handle user input and output operations

D. To store data persistently in databases

Solution

1. Step 1: Understand the role of structural patterns

   Structural patterns focus on how classes and objects are composed to form larger structures.

2. Step 2: Identify the main goal

   The main goal is to simplify the design by making relationships flexible and clear.

3. Final Answer:

   To simplify system design by organizing how classes relate -> Option A

4. Quick Check:

   Structural patterns simplify class relationships [OK]

Hint: Structural patterns simplify class connections [OK]

Common Mistakes:

• Confusing structural patterns with performance optimization
• Thinking structural patterns manage data storage
• Mixing structural patterns with user interface handling

2. Which of the following is a correct example of a structural pattern that organizes class relationships?

easy

A. Factory pattern

B. Singleton pattern

C. Adapter pattern

D. Observer pattern

Solution

1. Step 1: Recall common structural patterns

   Adapter, Decorator, and Composite are examples of structural patterns.

2. Step 2: Match options to pattern types

   Adapter is a structural pattern; Singleton is creational; Observer is behavioral; Factory is creational.

3. Final Answer:

   Adapter pattern -> Option C

4. Quick Check:

   Adapter = Structural pattern [OK]

Hint: Adapter is a classic structural pattern [OK]

Common Mistakes:

• Confusing creational patterns with structural ones
• Selecting Observer which is behavioral
• Choosing Factory which is creational

3. Given the following class structure using the Decorator pattern, what is the main benefit of this design?

class Coffee {
  cost() { return 5; }
}
class MilkDecorator {
  constructor(coffee) { this.coffee = coffee; }
  cost() { return this.coffee.cost() + 2; }
}

medium

A. It speeds up the cost calculation by caching results

B. It allows adding features dynamically without changing original classes

C. It restricts the coffee class from being extended

D. It stores coffee objects in a database

Solution

1. Step 1: Analyze the Decorator pattern usage

   The MilkDecorator wraps a Coffee object and adds extra cost dynamically.

2. Step 2: Understand the benefit

   This design allows adding new features (like milk) without modifying the original Coffee class.

3. Final Answer:

   It allows adding features dynamically without changing original classes -> Option B

4. Quick Check:

   Decorator adds features dynamically [OK]

Hint: Decorator adds features without changing original class [OK]

Common Mistakes:

• Thinking it caches results for speed
• Believing it restricts class extension
• Assuming it handles data storage

4. Identify the error in this Adapter pattern implementation:

class OldSystem {
  oldRequest() { return 'Old response'; }
}
class Adapter {
  constructor(oldSystem) { this.oldSystem = oldSystem; }
  request() { return this.oldSystem.request(); }
}

medium

A. Adapter should inherit from OldSystem

B. OldSystem class should not have any methods

C. Constructor is missing in OldSystem

D. Adapter calls a non-existent method 'request' instead of 'oldRequest'

Solution

1. Step 1: Check method calls in Adapter

   Adapter calls this.oldSystem.request(), but OldSystem has only oldRequest() method.

2. Step 2: Identify the mismatch

   The Adapter should call oldRequest() to adapt it to request().

3. Final Answer:

   Adapter calls a non-existent method 'request' instead of 'oldRequest' -> Option D

4. Quick Check:

   Method name mismatch in Adapter [OK]

Hint: Check method names carefully in Adapter calls [OK]

Common Mistakes:

• Assuming inheritance is required in Adapter
• Thinking OldSystem should be empty
• Ignoring method name differences

5. You need to design a system where multiple objects form a tree structure and clients treat individual objects and compositions uniformly. Which structural pattern best organizes this relationship?

hard

A. Composite pattern

B. Facade pattern

C. Proxy pattern

D. Bridge pattern

Solution

1. Step 1: Understand the problem requirements

   The system needs to treat individual objects and groups (tree structure) uniformly.

2. Step 2: Match with structural patterns

   The Composite pattern allows composing objects into tree structures and clients treat them the same.

3. Step 3: Eliminate other options

   Facade simplifies interfaces, Proxy controls access, Bridge separates abstraction from implementation; none fit the tree structure need.

4. Final Answer:

   Composite pattern -> Option A

5. Quick Check:

   Tree structure uniform treatment = Composite [OK]

Hint: Composite handles tree structures uniformly [OK]

Common Mistakes:

• Confusing Facade with Composite
• Choosing Proxy for access control only
• Mixing Bridge with structural composition