Hubungan Komposisi OOP dalam C++

Apakah Hubungan Komposisi (Composition Relationship) Objek?

- In object-oriented programming (OOP), object composition refers to building complex objects by combining simpler ones.

- Imagine assembling a mobile phone: it consists of various components like a camera, battery, screen, and sensors. Each of these components is a simpler object.

- The process of creating a mobile phone by putting together these components is an example of object composition.

Bagaimana ia berfungsi?

- In C++, we create classes to define objects. A class can contain other objects as its members.

- Consider two classes:

$$A~and~B$$

- B is a complex class that uses objects of class A as its data members.

- This relationship is called composition.

Here’s a simple example:

#include <iostream>

using namespace std;

class A {

public:

    int x;

    A() { x = 0; }

    A(int a) {

        cout << "Constructor A (int a) is invoked" << endl;

        x = a;

    }

};

class B {

    int data;

    A objA; // Composition: B has an object of class A

public:

    B(int a) : objA(a) {

        data = a;

    }

    void display() {

        cout << "Data in object of class B = " << data << endl;

        cout << "Data in member object of class A in class B = " << objA.x;

    }

};

int main() {

    B objb(25);

    objb.display();

    return 0;

}

In this example:

• B contains an object of class A (composition).
• B has-a A object.
• In UML, [  B ]

  ◆

  -------[  A  ]
• When we create an instance of B, it also creates an instance of A.
• The data in objA is part of the whole object B.

Jenis Komposisi Objek

There are two basic subtypes:

1. Composition:

•  Part-whole relationship.
• A part belongs to only one object at a time.
• The part’s existence is managed by the whole object.
• Example: A car’s engine is a composition.

1. Aggregation:

• Parts can belong to multiple objects simultaneously.
• The whole object isn’t responsible for the parts’ existence.
• Example: A library and its books (books can be borrowed by different readers).

Remember, composition models relationships where one object has-a relationship with another.