[!INDEX]

1. def - is a - subclass inherit...
2. def - has a - one class contains or is composed ...
3. def - composition ( strong form, life cycle, owned)
4. def - aggregation ( week form, not - life cycle, owned)
5. is a code dog subclass of animal ( dog is a animal) code
6. code : composition = car, engine
7. code : aggregation = car, engine

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1. Def. - is a - subclass inherit...

[!NOTE]

1. where one class (subclass or child class) inherits the properties and behaviors of another class (superclass or parent class).
2. In Java, the concepts of "is-a" relationship and "has-a" relationship are fundamental to understanding object-oriented programming principles like inheritance and composition.

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2. def. - has a - one class contains or is composed ...

[!NOTE]

1. Both composition and aggregation represent "has-a" relationships where one class contains or is composed of one or more instances of other classes.
2. one class contains a reference to another class. This relationship is established using instance variables. It indicates that an object of one class has an object of another class.

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3. def. - composition ( strong form, life cycle, owned)

[!NOTE]

1. strong form of association where the contained object (part) is owned by the container object (whole). If the container object is destroyed, the contained object is also destroyed.
2. Strong Ownership: The container class owns the contained class. The contained object cannot exist independently of the container.
3. Lifecycle Dependency: The lifecycle of the contained object is tightly bound to the lifecycle of the container object.

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4. def. - aggregation ( week form, not - life cycle, owned)

[!NOTE]

1. weaker form of association where the contained object can exist independently of the container object. The container and the contained objects have their own lifecycles.
2. Key Characteristics:
3. Weak Ownership: The container class references the contained class but does not own it. The contained object can exist independently of the container.
4. Independent Lifecycle: The lifecycle of the contained object is independent of the container object.

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5. is a code dog subclass of animal ( dog is a animal) code

// Superclass
class Animal {
    void eat() {
        System.out.println("This animal eats food.");
    }
}
// Subclass
class Dog extends Animal {
    void bark() {
        System.out.println("The dog barks.");
    }
}
public class Main {
    public static void main(String[] args) {
        Dog myDog = new Dog();
        myDog.eat(); // Inherited method from Animal
        myDog.bark(); // Method of Dog
    }
}

[!NOTE]

1. In this example, Dog is a subclass of Animal. Therefore, a Dog is an Animal, establishing an "is-a" relationship.

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6. code : composition = car, engine

class Engine {
    void start() {
        System.out.println("Engine starts.");
    }
}
class Car {
    private Engine engine;
    Car() {
        this.engine = new Engine(); // Creating and owning the Engine instance
    }
    void startCar() {
        engine.start();
        System.out.println("Car starts.");
    }
}
public class Main {
    public static void main(String[] args) {
        Car car = new Car();
        car.startCar();
    }
}

[!NOTE]

1. In this example, Car has a strong ownership of Engine. The Engine instance is created within the Car constructor and cannot exist without the Car.
2. the car is container , coz it contains /own the engine object.
3. if car object destroy , cant access the engine object, means only car object can access the engine members
4. owns का मतलब contained object की life cycle को container का object manage करेगा | मतलब creation , existence और destruction ये तीनो container object पर निर्भर करता है |

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7. code : aggregation = car, engine

class Engine {
    void start() {
        System.out.println("Engine starts.");
    }
}
class Car {
    private Engine engine;
    Car(Engine engine) {
        this.engine = engine; // Using an existing Engine instance
    }
    void startCar() {
        engine.start();
        System.out.println("Car starts.");
    }
}
public class Main {
    public static void main(String[] args) {
        Engine engine = new Engine();
        Car car = new Car(engine); // Passing an existing Engine instance
        car.startCar();
    }
}

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[!NOTE]

1. In this example, Car aggregates Engine. The Engine instance is created outside the Car and passed to the Car constructor. The Engine can exist independently of the Car.
2. its mean that another class can easily access the engine fields and members.
3. Composition/Aggregation - दोनों का मतलब एक class contain करती है दुसरी क्लास का reference बिना extends के method को कैसे access करे

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[!approach]

1. create engine { with start }and car class { with startCar() }
2. in main class , turn on car using startCar method(). -- but car doesn't has engine
3. two way to achieve

COMPOSITION

1. create engine instance variable in car and initialized it with new instance of Engine class.
2. this instance can now call Engine's class start method.

AGGREGATION

1. create new instance in main method and pass it to car parameterized constructor
2. this instance can now call Engine's class start method.