What is Composition?

Posted in: 10 Tricky Java Interview Questions,15 Most Java Interview Questions for Experienced professionals.,Java interview questions Composition is a special type of aggregation relationship with a difference that its the compulsion for the OtherClass object to exist for the existence of MyMainClass.

import java.util.ArrayList;

public class Aggregation 
{
 public static void main(String[] args)
  {
    MusicPlayer player = new MusicPlayer();
    Car car = new Car();
    car.addPlayer(player);
  }
}

/**
* Client, Aggregate, Whole
*/
class Car {
private ArrayList players;

public Car() {
// players list is empty, we can attach players via addPlayer(), so
// that car CONTAINS players, however our car object is not dependant
// on player for initialization – we can initialize car objects even
// if we have no intention to put player into them
players = new ArrayList();
}

public void addPlayer(MusicPlayer p)
{
 players.add(p);
}
}

/**
* Dump MusicPlayer class
*/
class MusicPlayer 
{
// Code ...
}