Composition, Aggregation, and Association in Java

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In the realm of object-oriented programming, the relationships between classes play a pivotal role in designing robust and maintainable software systems. Three key concepts that govern these relationships are Composition, Aggregation, and Association. In this blog post, we will explore the intricacies of these concepts, exploring their meanings and implications through real-world examples in Java.

Composition: Whole-Part Relationship

Composition represents a strong “whole-part” relationship between two classes, where one class (the whole) is composed of one or more instances of another class (the part). The part objects are tightly bound to the whole and have no independent existence outside it.

Example: Car and Engine

Consider a Car class that is composed of an Engine class. The Engine is an integral part of the Car, and when the Car is destroyed, the Engine is also disposed of.

class Engine {
    // Engine attributes and methods
}

class Car {
    private Engine engine;
    public Car() {
        engine = new Engine();
    }
    // Car attributes and methods
}

Aggregation: Has-A Relationship

Aggregation is a “has-a” relationship between classes, where one class (the whole) has a reference to another class…