Aggregation in Java

Aggregation in Java allows us to provide a reference for one class within another class. In other words, it supports a one-way relationship and implements a HAS-A relation. This is in contrast to the java inheritance concept that supports IS-A relation.

 

When two classes have a HAS-A relation, we say it implements aggregation. One best example we can think of is "Employee has a Car". We say this is unidirectional since a car cannot have an employee and only an employee can have a car.

 

Before we understand this with an example, let see why we need to use aggregation.

Usage of Aggregation in java

 

- Provides reusability of code

- We can directly access the methods and variables of the reference class

- Implements HAS-A relation

 

Example of Aggregation

Let us see how we can implement "Employee has a Car" in java using the aggregation concept. We create 2 classes Car and Employee. In the Employee class, we create a reference to the Car class by creating an object. Hence using this car object we can access all the properties of the Car class. So the Employee class has a unidirectional relationship with the Car class that implements aggregation.

 

This is a realtime example of aggregation where the company can track which employees are coming in their own vehicle to provide vehicle pass.

class Car {

String carname;

String color;

String regno;

 

Car(String carname, String color, String regno) {

this.carname = carname;

this.color = color;

this.

 

www.tutorialcup.com/java/aggregation-in-java.htm

Done