Aggregation and Composition - OOPS

 

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Sure! Let’s break down the concepts of aggregation and composition in Java with simple examples.

Aggregation

Aggregation is a type of association where one class contains a reference to another class. It represents a “has-a” relationship but with a weaker bond. The contained object can exist independently of the container object.

Example:

Consider a Library and Book:

Java

class Book {
    String title;
    String author;

    Book(String title, String author) {
        this.title = title;
        this.author = author;
    }
}

class Library {
    String name;
    List<Book> books;

    Library(String name, List<Book> books) {
        this.name = name;
        this.books = books;
    }

    void displayBooks() {
        for (Book book : books) {
            System.out.println("Title: " + book.title + ", Author: " + book.author);
        }
    }
}

public class Main {
    public static void main(String[] args) {
        Book book1 = new Book("1984", "George Orwell");
        Book book2 = new Book("To Kill a Mockingbird", "Harper Lee");

        List<Book> books = new ArrayList<>();
        books.add(book1);
        books.add(book2);

        Library library = new Library("City Library", books);
        library.displayBooks();
    }
}

AI-generated code. Review and use carefully. More info on FAQ.

In this example, Library has a list of Book objects. The Book objects can exist independently of the Library object.

Composition

Composition is a stronger form of association where one class contains another class, and the contained class cannot exist independently of the container class. It represents a “part-of” relationship.

Example:

Consider a House and Room:

Java

class Room {
    String name;

    Room(String name) {
        this.name = name;
    }
}

class House {
    String address;
    List<Room> rooms;

    House(String address) {
        this.address = address;
        this.rooms = new ArrayList<>();
        rooms.add(new Room("Living Room"));
        rooms.add(new Room("Bedroom"));
    }

    void displayRooms() {
        for (Room room : rooms) {
            System.out.println("Room: " + room.name);
        }
    }
}

public class Main {
    public static void main(String[] args) {
        House house = new House("123 Main St");
        house.displayRooms();
    }
}

AI-generated code. Review and use carefully. More info on FAQ.

In this example, House contains Room objects. The Room objects cannot exist independently of the House object. If the House object is destroyed, the Room objects are also destroyed.

Summary

• Aggregation: A “has-a” relationship with a weaker bond. The contained object can exist independently.
• Composition: A “part-of” relationship with a stronger bond. The contained object cannot exist independently.