Where is it better to apply inheritance and…

Inheritance is used when there is an "is-a" relationship between classes. It is used for code reuse and establishing class hierarchies. Example: Cat inherits from Animal.

Association is used when there is a "has-a" or "uses-a" relationship between classes. It is a weaker relationship than inheritance. It is used to establish connections between objects. Association can be:

Aggregation: The "whole" consists of "parts", but "parts" can exist independently. Example: Library has Books. Books can exist outside the library.
Composition: The "whole" fully controls the lifecycle of the "parts". "Parts" cannot exist without the "whole". Example: Room has a Wall. The wall cannot exist without the room.

Here are code examples:

// Inheritance
public class Animal {
    public void eat() {
        System.out.println("Animal eats");
    }
}

public class Cat extends Animal {
    public void purr() {
        System.out.println("Cat purrs");
    }
}

// Aggregation
import java.util.List;
import java.util.ArrayList;

public class Book {
    private String title;

    public Book(String title) {
        this.title = title;
    }

    public String getTitle() {
        return title;
    }
}

public class Library {
    private List<Book> books;

    public Library() {
        this.books = new ArrayList<>();
    }

    public void addBook(Book book) {
        this.books.add(book);
    }

    public List<Book> getBooks() {
        return books;
    }
}

// Composition
public class Wall {
    private String material;

    public Wall(String material) {
        this.material = material;
    }

    public String getMaterial() {
        return material;
    }
}

public class Room {
    private Wall wall; // Composition

    public Room(String wallMaterial) {
        this.wall = new Wall(wallMaterial);
    }

    public Wall getWall() {
        return wall;
    }
}

Overall, it is preferable to use association (especially composition) instead of inheritance when possible. This promotes better flexibility and weaker coupling between classes. Excessive use of inheritance can lead to rigid hierarchies.

Where is it better to apply inheritance and association in programming?