What’s the difference between Association, Aggregation,...

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What’s the difference between Association, Aggregation, and Composition in Java?

· java,video

🚀 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)

Learn Java ☕