Every strong system you build starts with strong fundamentals.
Most people read these concepts. Few actually remember them in interviews.
Here’s the simplest way to lock them in forever 👇
1. Association — “Just knowing each other”
Two objects are related, but can exist independently.
Example:
A Teacher and a Student
A teacher teaches students
Both can exist without each other
Memory trick:
People in the same WhatsApp group
2. Aggregation — “Has-a (loose ownership)”
One object contains another, but they can still live separately.
Example:
A Team has Players
If the team is deleted, players still exist
Memory trick:
Company hires employees (they can resign)
3. Composition — “Has-a (strong ownership)”
One object completely owns another. If parent dies, child dies.
Example:
A House has Rooms
Destroy the house → rooms are gone
Memory trick:
Human body → organs
4. Inheritance — “Is-a relationship”
One class inherits properties/behavior from another.
Example:
A Dog is an Animal
Dog gets all common animal traits
Memory trick:
Child inherits traits from parents
Quick Sheet
- Association → uses
- Aggregation → has (weak)
- Composition → has (strong)
- Inheritance → is
Interview Hack
- Can child exist without parent? → YES → Aggregation → NO → Composition
- Is it “is-a”? → YES → Inheritance
- Otherwise? → Association
And About Cracking Big Companies...
Interviews don’t test memory, they test clarity — this is your edge. So Today it’s OOP relationships — tomorrow it’s cracking your dream job 🚀
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