Difference between Composition and Inheritance

Last Updated on August 5, 2024 by Abhishek Sharma

In object-oriented programming (OOP), composition and inheritance are two fundamental concepts used to build complex systems from simpler ones. Both serve to create relationships between classes, but they do so in different ways and with distinct implications. Understanding the difference between composition and inheritance is crucial for designing robust, maintainable, and flexible software systems. This article delves into the definitions, uses, and key differences between these two concepts, helping you make informed decisions in your software design.

What is Composition?

Composition is a design technique that allows a class to be composed of objects of other classes as its members. The objects provide the functionality needed by the class, and the class uses these objects to perform its tasks. Composition enables greater flexibility in code design, as it allows developers to build complex objects from smaller, simpler objects. It also allows for easy modification and replacement of individual objects, without affecting the entire class.

Code Implementation

class Engine {
    public void start() {
        System.out.println("Engine started.");
    }
}

class Car {
    private Engine engine;

    public Car() {
        this.engine = new Engine();
    }

    public void start() {
        this.engine.start();
        System.out.println("Car started.");
    }
}

public class Main {
    public static void main(String[] args) {
        Car car = new Car();
        car.start();
    }
}

Output

Engine started.
Car started.

Explanation
In this example, we have two classes, Engine, and Car. The Engine class has a start() method that prints "Engine started." to the console. The Car class has a private instance variable engine of type Engine, which is initialized in the constructor. The Car class also has a start() method that calls the start() method of the engine object and then prints "Car started." to the console.

The Main class contains the main() method, which creates a new Car object and calls its start() method. When the program is run, the following output is produced: This example demonstrates composition in Java, where the Car class is composed of an Engine object. The Car class uses the Engine object to provide the functionality needed to start the car. By using composition, we have created a more modular and flexible design, as we can easily modify or replace the Engine object without affecting the Car class as a whole.

What is Inheritance?

Inheritance is a powerful tool for implementing code reuse in object-oriented programming. It is the functionality that allows one object to take on the characteristics of one or more other objects. In C++, inheritance means that you can create classes that inherit attributes from other classes. This implies that you specialize a class in order to establish an is-a relationship between the classes, resulting in a strong coupling between the base and derived classes. Because new classes are created from existing classes, inheritance promotes code reusability. Class inheritance also makes it easier to modify the reused implementation. However, there are some disadvantages to class inheritance.

It is a property that enables a class to inherit properties and methods from a parent class. Inheritance allows developers to create new classes that are based on existing classes, thereby promoting code reuse and reducing duplication. Inheritance provides a more structured approach to code design, as it creates a hierarchy of classes where each subclass inherits properties and methods from its parent class.

Code Implementation

 class Animal {
    public void speak() {
        System.out.println("Animal speaks.");
    }
}

class Dog extends Animal {
    public void speak() {
        System.out.println("Dog barks.");
    }
}

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

public class Main {
    public static void main(String[] args) {
        Animal animal = new Animal();
        animal.speak();

        Dog dog = new Dog();
        dog.speak();

        Cat cat = new Cat();
        cat.speak();
    }
}

Output

Animal speaks.
Dog barks.
Cat meows.

Explanation
In this example, we have an Animal class with a speak() method that prints "Animal speaks." to the console. We also have two subclasses, Dog and Cat, which extend the Animal class and override the speak() method to print "Dog barks." and "Cat meows." to the console, respectively.

When we create objects of each class and call their speak() method in the main() method, the following output is producedThis example demonstrates how inheritance enables us to create subclasses that share properties and methods with their parent class but can also add new properties and methods of their own. In this case, both the Dog and Cat classes inherit the speak() method from the Animal class but also add their unique behavior.

Difference between Composition and Inheritance

Here we have the difference between composition and inheritance

Conclusion
Composition and inheritance are powerful tools in object-oriented programming, each with its own strengths and appropriate use cases. Inheritance facilitates code reuse and polymorphism by establishing an "is-a" relationship between classes. However, it can lead to tight coupling and less flexible designs. Composition, on the other hand, promotes flexibility and reusability by building classes from other classes, establishing a "has-a" relationship. While inheritance should be used judiciously to avoid complications in complex hierarchies, composition offers a more modular and maintainable approach to software design. Understanding when and how to use each concept is key to creating efficient and scalable object-oriented systems.

Frequently Asked Question related to the difference between composition and inheritance

Here we have FAQs on the difference between composition and inheritance

1. What is inheritance in object-oriented programming?
Inheritance is an OOP concept where a new class (derived or subclass) inherits properties and behaviors (methods) from an existing class (base or superclass), establishing an "is-a" relationship.

2. What is composition in object-oriented programming?
Composition is an OOP concept where a class is composed of one or more objects from other classes, establishing a "has-a" relationship. It involves including instances of other classes as member variables.

3. When should I use inheritance over composition?
Use inheritance when there is a clear hierarchical relationship and the subclass needs to inherit and possibly extend the behavior of the superclass. It is suitable for scenarios where classes share a common interface or base implementation.

4. When is composition more appropriate than inheritance?
Composition is more appropriate when you want to build complex objects from simpler ones and when you need more flexibility and modularity. It is preferred when the relationship between classes is not strictly hierarchical.

5. What are the drawbacks of using inheritance?
Drawbacks of inheritance include tight coupling between the base and derived classes, reduced flexibility, and the potential for a fragile base class problem, where changes to the base class can impact all derived classes.