Coupling vs Cohesion

Both are software design principles that help you build maintainable and robust systems, but they focus on different aspects.

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1️⃣ Cohesion

🔑 Definition:

• Cohesion measures how closely related the responsibilities of a single module/class are.
• A module is highly cohesive if all its parts are focused on a single task or purpose.

🖼 Example:

• High cohesion:

  Class: InvoiceGenerator
  Methods: generateInvoice(), calculateTotal(), formatInvoice()
  

  • Everything in the class is related to invoice generation.

• Low cohesion:

  Class: Utility
  Methods: generateInvoice(), sendEmail(), saveToDB(), drawChart()
  

  • The class does many unrelated tasks → harder to maintain and reuse.

✅ Key Idea:

“Keep related things together.”

• High cohesion → easier to understand, maintain, and test.

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2️⃣ Coupling

🔑 Definition:

• Coupling measures how dependent one module/class is on another.
• Low coupling is desirable → modules can work independently.

🖼 Example:

• High coupling:

  Class A directly modifies internal data of Class B
  Class A depends on Class B's private methods
  

  • Changes in B → break A → hard to maintain.

• Low coupling:

  Class A uses an interface of Class B
  Class A doesn’t care about B’s internal implementation
  

  • B can change internally → A unaffected → more flexible.

✅ Key Idea:

“Reduce dependencies between modules.”

• Low coupling → easier to extend, modify, and reuse modules.

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3️⃣ Coupling vs Cohesion – Quick Comparison

Aspect	Cohesion	Coupling
Focus	Within a single module/class	Between multiple modules/classes
Goal	Make module focused & clear	Make modules independent
High/Low Good?	High cohesion is good	Low coupling is good
Example	InvoiceGenerator only handles invoices	Module depends on another module

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4️⃣ Analogy

• Cohesion: A team where all members work on the same project → efficient and clear.
• Coupling: Multiple teams independent of each other → one team’s changes don’t break others.

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💡 Rule of Thumb:

• Design modules/classes with high cohesion and low coupling → leads to clean, maintainable, and scalable code.

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