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🚀 Java Interview Questions – Episode 4
💡 What’s the difference between Association, Aggregation, and Composition in Java?

These are all types of object relationships in OOP —
but they differ in strength and lifespan dependency.
Let’s break it down:

🔹 Association → A general relationship between two classes.
Example: A Teacher works in a School.
Both can exist independently.
class School {
String name;

void employ(Teacher teacher) {
System.out.println(teacher.name + " works at " + this.name);
}
}

🔹 Aggregation → A "has-a" relationship, but with loose coupling.
Example: A Department has Professors,
but professors can exist without the department.
🧩 Think of it as weak ownership.
class Department {
List〈Professor〉 professors;

Department(List〈Professor〉 profs) {
this.professors = profs;
}
}

🔹 Composition → A strong "has-a" relationship with tight coupling.
Example: A House has Rooms.
If the house is destroyed, so are the rooms.
🔒 This is strong ownership, with lifecycle dependency.
class House {
private List〈Room〉 rooms = new ArrayList〈〉();

House() {
rooms.add(new Room());
rooms.add(new Room());
}
}

🧠 TL;DR:
Composition 〉 Aggregation 〉 Association (in terms of coupling and dependency)

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