Concept · Core

Cohesion & Coupling

Aim for HIGH cohesion (a class’s parts belong together) and LOW coupling (classes barely depend on each other). It’s the master dial behind every other principle.

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step 1 / 7

1/2Low cohesion, high coupling

Utils

+ parseDate()

+ sendEmail()

+ calcTax()

+ resizeImg()

Orders

Billing

Shipping

Low cohesion, high coupling

 1class Utils {                 // grab-bag — does everything
 2    parseDate(); sendEmail(); calcTax(); resizeImg();
 3}
 4 
 5Orders   → Billing → Shipping → Orders   // tangled web

State

cohesionlow

✦

Meet the Utils class: parseDate, sendEmail, calcTax, resizeImg. These methods have NOTHING to do with each other — a grab-bag. That’s LOW cohesion.