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Java-programs/aggregation.java at main · tejaspundpal/Java-programs · GitHub

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// Java Program to Illustrate Difference between

// Aggregation and Composition

// Importing I/O classes

import java.io.*;

// Class 1

// Engine class which will

// be used by car. so 'Car'

// class will have a field

// of Engine type.

class Engine {

// Method to starting an engine

public void work()

{

// Print statement whenever this method is called

System.out.println(

"Engine of car has been started ");

}

}

// Class 2

// Engine class

final class Car {

// For a car to move,

// it needs to have an engine.

// Composition

private final Engine engine;

// Note: Uncommented part refers to Aggregation

// private Engine engine;

// Constructor of this class

Car(Engine engine)

{

// This keywords refers to same instance

this.engine = engine;

}

// Method

// Car start moving by starting engine

public void move()

{

// if(engine != null)

{

// Calling method for working of engine

engine.work();

// Print statement

System.out.println("Car is moving ");

}

}

}

// Class 3

// Main class

class aggregations {

// Main driver method

public static void main(String[] args)

{

// Making an engine by creating

// an instance of Engine class.

Engine engine = new Engine();

// Making a car with engine so we are

// passing a engine instance as an argument

// while creating instance of Car

Car car = new Car(engine);

// Making car to move by calling

// move() method inside main()

car.move();

}

}

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