SOLID principles in Software Engineering - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to identify the SOLID principle that states a class should have only one reason to change.

Software Engineering

The [1] principle means a class should have only one reason to change.

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

ASingle Responsibility

BLiskov Substitution

COpen/Closed

DDependency Inversion

Attempts:

3 left

💡 Hint

Common Mistakes

Confusing Single Responsibility with Open/Closed principle.

Thinking it relates to inheritance or dependencies.

The Single Responsibility Principle (SRP) states that a class should have only one reason to change, meaning it should have only one job or responsibility.

2fill in blank

medium

Complete the sentence to describe the Open/Closed principle.

Software Engineering

The Open/Closed principle means software entities should be open for [1] but closed for [2].

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

Amodification

Babstraction

Cinheritance

Dextension

Attempts:

3 left

💡 Hint

Common Mistakes

Choosing 'modification' for both blanks.

Confusing extension with inheritance.

The Open/Closed principle states that software entities should be open for extension but closed for modification, allowing behavior to be added without changing existing code.

3fill in blank

hard

Fix the error in the description of the Liskov Substitution principle.

Software Engineering

The Liskov Substitution principle means that objects of a superclass should be replaceable with objects of a [1] without affecting the correctness of the program.

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

Aunrelated class

Bdifferent class

Csubclass

Dparent class

Attempts:

3 left

💡 Hint

Common Mistakes

Choosing unrelated or different classes instead of subclasses.

Misunderstanding the concept as unrelated to inheritance.

The Liskov Substitution principle states that objects of a superclass should be replaceable with objects of a subclass without breaking the program.

4fill in blank

hard

Fill both blanks to complete the Dependency Inversion principle statement.

Software Engineering

High-level modules should not depend on [1] modules. Both should depend on [2].

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

Alow-level

Bconcrete

Cabstractions

Dinterfaces

Attempts:

3 left

💡 Hint

Common Mistakes

Confusing concrete with abstractions.

Thinking high-level depends directly on concrete modules.

The Dependency Inversion principle says that high-level modules should not depend on low-level modules. Instead, both should depend on abstractions to reduce coupling.

5fill in blank

hard

Fill all three blanks to complete the statement about the Interface Segregation principle.

Software Engineering

Clients should not be forced to depend on interfaces they do not [1]. Instead, many client-specific [2] are better than one general [3].

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

Aimplement

Binterfaces

Cinterface

Dinherit

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'inherit' instead of 'implement'.

Confusing interface (singular) with interfaces (plural).

The Interface Segregation principle states that clients should not be forced to implement interfaces they do not use. It is better to have many client-specific interfaces than one general interface.

Practice

1. Which of the following best describes the Single Responsibility Principle (SRP) in SOLID?

easy

A. A class should have only one reason to change.

B. A class should inherit from multiple classes.

C. Functions should have multiple responsibilities.

D. Objects should be tightly coupled.

Solution

1. Step 1: Understand SRP definition

   The Single Responsibility Principle states that a class should have only one reason to change, meaning it should have one job or responsibility.

2. Step 2: Evaluate options

   A class should have only one reason to change.: A class should have only one reason to change. matches this definition exactly. Options B, C, and D contradict the principle by suggesting multiple responsibilities or tight coupling.

3. Final Answer:

   A class should have only one reason to change. -> Option A

4. Quick Check:

   SRP = One responsibility [OK]

Hint: SRP means one class, one job only [OK]

Common Mistakes:

• Thinking SRP allows multiple responsibilities
• Confusing SRP with inheritance rules
• Believing tight coupling is allowed

2. Which of the following is the correct syntax to express the Open/Closed Principle (OCP)?

easy

A. Software entities should be open for modification but closed for extension.

B. Software entities should be closed for both extension and modification.

C. Software entities should be open for both extension and modification.

D. Software entities should be open for extension but closed for modification.

Solution

1. Step 1: Recall OCP definition

   The Open/Closed Principle states that software entities should be open for extension but closed for modification, meaning you can add new features without changing existing code.

2. Step 2: Match options to definition

   Software entities should be open for extension but closed for modification.: Software entities should be open for extension but closed for modification. correctly states this principle. Software entities should be open for modification but closed for extension. reverses the terms, and options B and D contradict the principle.

3. Final Answer:

   Software entities should be open for extension but closed for modification. -> Option D

4. Quick Check:

   OCP = Open extension, closed modification [OK]

Hint: OCP means add features, don't change old code [OK]

Common Mistakes:

• Mixing up 'open for extension' and 'open for modification'
• Thinking OCP allows changing existing code freely
• Confusing OCP with SRP

3. Consider this code snippet applying the Liskov Substitution Principle (LSP):

class Bird:
    def fly(self):
        return "Flying"

class Penguin(Bird):
    def fly(self):
        return "Cannot fly"

bird = Bird()
penguin = Penguin()
print(bird.fly())
print(penguin.fly())

What is the output of this code?

medium

A. "Flying" followed by "Cannot fly"

B. "Flying" followed by "Flying"

C. Runtime error due to method override

D. "Cannot fly" followed by "Flying"

Solution

1. Step 1: Analyze Bird and Penguin classes

   Bird has a fly method returning "Flying". Penguin overrides fly to return "Cannot fly".

2. Step 2: Check print statements output

   bird.fly() returns "Flying". penguin.fly() returns "Cannot fly". So output is two lines: "Flying" then "Cannot fly".

3. Final Answer:

   "Flying" followed by "Cannot fly" -> Option A

4. Quick Check:

   bird.fly() = Flying, penguin.fly() = Cannot fly [OK]

Hint: Overridden methods can change output but not cause errors [OK]

Common Mistakes:

• Assuming penguin.fly() returns "Flying"
• Expecting runtime error from override
• Confusing method outputs order

4. Identify the error in this code violating the Interface Segregation Principle (ISP):

class WorkerInterface:
    def work(self): pass
    def eat(self): pass

class Robot(WorkerInterface):
    def work(self):
        print("Working")
    def eat(self):
        raise Exception("Robots don't eat")

medium

A. Robot class must implement eat() with a print statement.

B. WorkerInterface should have only one method.

C. Robot class should not implement eat() if it doesn't apply.

D. No error; this code follows ISP.

Solution

1. Step 1: Understand ISP

   Interface Segregation Principle says clients should not be forced to depend on methods they do not use.

2. Step 2: Analyze Robot class

   Robot implements eat() but raises an exception because it doesn't eat. This violates ISP because Robot is forced to implement an irrelevant method.

3. Final Answer:

   Robot class should not implement eat() if it doesn't apply. -> Option C

4. Quick Check:

   ISP forbids unused methods in interfaces [OK]

Hint: ISP means no forced unused methods [OK]

Common Mistakes:

• Thinking raising exception is acceptable
• Believing interface must have only one method
• Assuming no error if code runs

5. You have a payment system where new payment methods are added frequently. Which SOLID principle helps you design the system so you can add new payment types without changing existing code?

hard

A. Single Responsibility Principle

B. Open/Closed Principle

C. Liskov Substitution Principle

D. Dependency Inversion Principle

Solution

1. Step 1: Identify the problem

   The system needs to add new payment methods often without modifying existing code.

2. Step 2: Match with SOLID principles

   The Open/Closed Principle states software should be open for extension but closed for modification, exactly fitting this need.

3. Final Answer:

   Open/Closed Principle -> Option B

4. Quick Check:

   OCP = Add features without changing old code [OK]

Hint: OCP = add new without changing old [OK]

Common Mistakes:

• Confusing SRP with OCP
• Thinking LSP controls adding new types
• Assuming Dependency Inversion solves this