Aggregation is a relationship between classes which share "has-a" relationship. Aggregation can be defined as a "Whole-Part" relationship where part of the whole can exist without a whole. Ex: Person has an address. The address will exist even when the person doesn't.

																					
package com.visionjava;
public class Address {
    private String apartmentNumber;

    public String getApartmentNumber() {
    	return apartmentNumber;
    }

    public void setApartmentNumber(String apartmentNumber) {
	this.apartmentNumber = apartmentNumber;
    }	
}
									

											
package com.visionjava;
import com.visionjava.Address;

public class Person {
	private Address homeAddress;

	public Address getHomeAddress() {
		return homeAddress;
	}

	public void setHomeAddress(Address homeAddress) {
		this.homeAddress = homeAddress;
	}
	
	public static void main(String[] args){
		
		Address homeAddress = new Address();
		Person person = new Person();
		person.setHomeAddress(homeAddress);
		
	}
}

									

package com.visionjava;

public class LivingRoom {
	private double height;
	private double width;

	public double getWidth() {
		return width;
	}

	public void setWidth(double width) {
		this.width = width;
	}

	public double getHeight() {
		return height;
	}

	public void setHeight(double height) {
		this.height = height;
	}

}

package com.visionjava;

public class House {
	private int noOfRooms;

	private LivingRoom living = new LivingRoom();

	public int getNoOfRooms() {
		return noOfRooms;
	}

	public void setNoOfRooms(int noOfRooms) {
		this.noOfRooms = noOfRooms;
	}

	public LivingRoom getLiving() {
		return living;
	}

	public static void main(String[] args) {
		House house = new House();
		LivingRoom livingRoom = house.getLiving();
	}

}