In Java, aggregation is a type of relationship between two classes where one class has a reference to the other class, but the two classes are not dependent on each other. This relationship can be represented as a "has-a" relationship, where one class "has" another class.
Aggregation is often used to create complex objects from simpler objects. For example, a car is a complex object that is composed of simpler objects such as an engine, wheels, and chassis. In this case, the car "has" an engine, wheels, and a chassis, and these objects can be represented as separate classes.
To implement aggregation in Java, you can create a class representing the complex object and then create separate classes representing the simpler objects. The complex object class then includes references to the simpler object classes as instance variables.
Aggregation is a fundamental concept in Object-Oriented Programming (OOP). It is an association between two classes where one class is a "whole" entity, and the other is a "part" entity. This relationship is often described as a "has-a" relationship.
Here are some key characteristics of aggregation:
"Has-a" Relationship: Aggregation models a "has-a" relationship between two objects. For example, a Car class may have a Engine class. In this case, the Car "has-a" Engine.
Ownership: In an aggregation relationship, the "whole" doesn't necessarily have exclusive ownership of the "part". The "part" can belong to more than one "whole" object. For instance, a Course class (the "whole") could have Student objects (the "part"), but the same Student objects could belong to other Course objects as well.
Lifetime Independence: The lifecycle of the "part" object is independent of the "whole". This means that if the "whole" object is destroyed, the "part" object can continue to exist.
