Anti-patterns to avoid in LLD - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the 'God Object' anti-pattern?

The 'God Object' anti-pattern occurs when a single class or module tries to handle too many responsibilities, making it large, complex, and hard to maintain.

beginner

Why should 'Spaghetti Code' be avoided in system design?

'Spaghetti Code' refers to code with tangled and unstructured flow, making it difficult to understand, debug, and extend, leading to poor maintainability.

intermediate

Explain the 'Golden Hammer' anti-pattern.

The 'Golden Hammer' anti-pattern happens when a familiar tool or solution is overused for all problems, even when it's not the best fit, limiting flexibility and effectiveness.

intermediate

What problems arise from the 'Not Invented Here' syndrome?

'Not Invented Here' syndrome is when teams avoid using existing solutions and prefer building their own, causing wasted effort, delays, and potentially lower quality.

beginner

Describe the 'Premature Optimization' anti-pattern.

'Premature Optimization' is when developers focus on improving performance too early, before understanding real bottlenecks, which can waste time and complicate design unnecessarily.

Which anti-pattern involves a single class handling too many tasks?

A Golden Hammer

B Spaghetti Code

C God Object

D Not Invented Here

The God Object anti-pattern is when one class or module takes on too many responsibilities.

What is a key risk of the 'Golden Hammer' anti-pattern?

A Avoiding existing solutions

B Writing tangled and unstructured code

C Optimizing too early

D Using the wrong tool for every problem

Golden Hammer means overusing a familiar tool even when it's not suitable.

Which anti-pattern describes tangled, hard-to-follow code?

A Spaghetti Code

B God Object

C Premature Optimization

D Not Invented Here

Spaghetti Code is tangled and unstructured, making it hard to maintain.

What does the 'Not Invented Here' syndrome cause?

A Using too many tools

B Avoiding existing solutions and building new ones unnecessarily

C Writing large classes

D Optimizing before measuring

Not Invented Here means rejecting existing solutions and reinventing the wheel.

Why is 'Premature Optimization' harmful?

A It wastes effort on performance before knowing real issues

B It causes code to be tangled

C It leads to large classes

D It avoids using existing tools

Premature Optimization wastes time optimizing before identifying real bottlenecks.

List and explain three common anti-patterns to avoid in system design.

Think about problems caused by too much responsibility, tangled code, and early optimization.

Describe how the 'Not Invented Here' syndrome can impact a software project.

Consider team behavior and reuse of tools.

Practice

1. Which of the following best describes the God Object anti-pattern in system design?

easy

A. Separating data storage and business logic into different layers.

B. A system design where components are loosely connected and communicate via events.

C. A single component that handles too many responsibilities, making the system hard to maintain.

D. Using multiple small services to handle different tasks independently.

Solution

1. Step 1: Understand the God Object concept and compare options

   The God Object anti-pattern occurs when one component or class takes on too many responsibilities, leading to complex, hard-to-maintain code. A single component that handles too many responsibilities, making the system hard to maintain. matches this description exactly, while others describe good design practices.

2. Final Answer:

   A single component that handles too many responsibilities, making the system hard to maintain. -> Option C

3. Quick Check:

   God Object = Single overloaded component [OK]

Hint: God Object means one part does too much [OK]

Common Mistakes:

• Confusing God Object with microservices
• Thinking God Object is a good modular design
• Mixing God Object with event-driven architecture

2. Which of the following is an example of a hardcoding anti-pattern in system design?

easy

A. Storing configuration values directly inside the source code.

B. Using environment variables for configuration.

C. Separating configuration into external files.

D. Using feature flags to toggle functionality.

Solution

1. Step 1: Identify what hardcoding means and match options

   Hardcoding means embedding fixed values directly in the code, making changes difficult and error-prone. Storing configuration values directly inside the source code. shows storing config inside code, which is hardcoding. Others are best practices.

2. Final Answer:

   Storing configuration values directly inside the source code. -> Option A

3. Quick Check:

   Hardcoding = fixed values in code [OK]

Hint: Hardcoding means fixed values inside code [OK]

Common Mistakes:

• Confusing hardcoding with using environment variables
• Thinking external config files are hardcoding
• Mixing feature flags with hardcoding

3. Consider a system where all modules directly access a single shared database without any abstraction layer. What is the main anti-pattern here?

medium

A. Tight Coupling

B. God Object

C. Spaghetti Architecture

D. Event-Driven Design

Solution

1. Step 1: Analyze direct database access and identify the anti-pattern

   When modules directly access the database without abstraction, they become tightly coupled to the database schema. Tight Coupling means components depend heavily on each other, reducing flexibility and increasing maintenance difficulty.

2. Final Answer:

   Tight Coupling -> Option A

3. Quick Check:

   Direct DB access = Tight Coupling [OK]

Hint: Direct DB access causes tight coupling [OK]

Common Mistakes:

• Confusing tight coupling with God Object
• Thinking event-driven design fits here
• Mixing spaghetti architecture with tight coupling

4. You find a system where many components are tightly interconnected with complex dependencies, making it hard to change one without breaking others. What anti-pattern is this, and how can you fix it?

medium

A. God Object; merge all components into one big class.

B. Spaghetti Architecture; refactor to modular design with clear interfaces.

C. Hardcoding; move all values into source code.

D. Tight Coupling; remove all interfaces and use direct calls.

Solution

1. Step 1: Identify the anti-pattern from description and determine the fix

   Complex interdependencies causing fragility is typical of Spaghetti Architecture. Refactoring to modular design with clear interfaces reduces dependencies and improves maintainability.

2. Final Answer:

   Spaghetti Architecture; refactor to modular design with clear interfaces. -> Option B

3. Quick Check:

   Spaghetti Architecture = tangled dependencies [OK]

Hint: Tangled dependencies = spaghetti; modularize [OK]

Common Mistakes:

• Thinking God Object means merging components
• Confusing hardcoding with architecture issues
• Believing removing interfaces reduces coupling

5. A startup built a monolithic system with many hardcoded values and a God Object managing most logic. They want to scale and maintain it easily. What is the best approach to fix these anti-patterns?

hard

A. Ignore scalability and focus only on adding new features.

B. Keep the monolith but add more hardcoded values for speed.

C. Merge all logic into one bigger God Object for simplicity.

D. Refactor into microservices, externalize configuration, and split responsibilities into smaller components.

Solution

1. Step 1: Identify problems in current system and choose best solution to fix anti-patterns

   Monolith with hardcoded values and God Object causes poor scalability and maintainability. Refactoring into microservices splits responsibilities, externalizing config removes hardcoding, improving scalability and maintainability.

2. Final Answer:

   Refactor into microservices, externalize configuration, and split responsibilities into smaller components. -> Option D

3. Quick Check:

   Microservices + external config fix anti-patterns [OK]

Hint: Split monolith, externalize config, avoid God Object [OK]

Common Mistakes:

• Thinking bigger God Object improves simplicity
• Adding more hardcoding for speed
• Ignoring scalability needs