Understanding the Differences Between Inheritance and Polymorphism in Java

When it comes to Object-Oriented Programming (OOP) in Java, inheritance and polymorphism are two foundational concepts that serve distinct yet complementary purposes. Inheritance establishes a relationship between classes, allowing for code reuse, while polymorphism provides the flexibility for objects to take on multiple forms, adapting behavior based on context.

In this blog, you'll explore the key differences between inheritance in java and java's polymorphism, covering their nature, implementation techniques, and use cases. You'll gain insights into how these concepts work together to create scalable, maintainable, and flexible Java applications.

Key Differences Between Inheritance and Polymorphism

Inheritance and polymorphism are both essential concepts in object-oriented programming (OOP), but they serve different purposes, each contributing to the architecture and flexibility of software in unique ways. While inheritance creates relationships between classes to promote code reuse, polymorphism utilizes those relationships to introduce flexibility by allowing objects to take different forms and behaviors.

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Let’s break down the key differences between inheritance and polymorphism. You’ll also explore the nuances that can make your code more organized, adaptable, and powerful.

Also Read: Top 40 OOPs Interview Questions & Answers for 2025

Having outlined the main differences between inheritance and polymorphism, let’s focus on Inheritance in Java and explore its core mechanisms and usage in detail.

Inheritance is a key feature of object-oriented programming (OOP) in Java that allows one class to inherit properties and behaviors from another class. This concept serves as a foundation for code reusability and establishes a parent-child relationship between classes, where the child class (also known as the subclass) receives attributes and methods from the parent class (or superclass). 

While inheritance is focused on establishing shared functionality, it is important to also understand the differences between inheritance and polymorphism, as both play distinct roles in OOP.

Core Mechanism of Inheritance

Java inheritance works through a system where child classes are built on parent classes. The keyword 'extends' establishes this inheritance relationship in Java. When one class extends another, it gets access to the fields and methods of the parent class by forming an IS-A relationship. You can refer to upGrad’s Inheritance in Java Tutorial for an in-depth understanding of its core functions.

A child class receives these elements from its parent in the following three methods:

• Fields and methods marked as public or protected move to the child class, which can use them as if they were its own. For example, a parent class Vehicle with a method StartEngine () passes this method to all its child classes.
• Constructors in Java do not transfer through inheritance, but the child class must call the parent constructor. The child class uses the super keyword to reach the parent constructor and set up the base class parts.
• Private members stay in the parent class. The child class cannot see or use private items directly. This rule helps keep data safe and creates clear lines between classes.

Types of Inheritance Supported

Java allows single inheritance for classes. This means one class can extend only one parent class. This rule keeps the code clear and stops complex problems that come with multiple parent classes. Here are the main types of inheritance in Java:

• Single Inheritance: In single inheritance, a class can inherit from only one superclass. This is the most common and straightforward type of inheritance in Java, and it promotes simplicity in class hierarchies.
• Multilevel Inheritance: A class inherits from another class, which in turn inherits from another class. This creates a chain of inheritance. Each subclass inherits from its direct superclass as well as all ancestor classes.
• Hierarchical Inheritance: One class serves as the superclass for multiple subclasses. Several classes inherit from a single base class.

Though Java blocks direct multiple inheritance, a class can implement many interfaces. Each interface adds a contract of methods the class must create. This approach gives the benefits of multiple inheritance while avoiding its problems.

For example, a Car class extends Vehicle but can also implement interfaces like Insurable and Maintainable. This structure allows the Car class to inherit core vehicle features from its parent and add specific behaviors through interfaces.

The interface system creates a clean way to add features to classes. It helps write code that others can understand and change. This plays an important role in big projects where many programmers and teams work together.

Practical Java Examples

The Vehicle hierarchy shows how inheritance works in practice. This structure matches practical relationships between objects. A basic example shows these connections:

// Base class Vehicle
class Vehicle {
    String brand;
    String model;

    // Constructor to initialize Vehicle
    public Vehicle(String brand, String model) {
        this.brand = brand;
        this.model = model;
    }

    // Method to move the vehicle
    public void move() {
        System.out.println("The vehicle is moving.");
    }
}

// Derived class Car that extends Vehicle
class Car extends Vehicle {
    int numberOfDoors;

    // Constructor to initialize Car
    public Car(String brand, String model, int numberOfDoors) {
        super(brand, model); // Call the parent constructor to initialize brand and model
        this.numberOfDoors = numberOfDoors;
    }

    // Method specific to Car
    public void switchGear() {
        System.out.println("Switching gear.");
    }
}
// Derived class SportsCar that extends Car
class SportsCar extends Car {

    // Constructor to initialize SportsCar
    public SportsCar(String brand, String model, int numberOfDoors) {
        super(brand, model, numberOfDoors); // Call the parent constructor to initialize brand, model, and doors
    }

    // Method specific to SportsCar
    public void turboBoost() {
        System.out.println("Activating turbo boost!");
    }
}

// Testing the classes
public class Main {
    public static void main(String[] args) {
        // Create a SportsCar object
        SportsCar sportsCar = new SportsCar("Ferrari", "488", 2);

        // Call methods from the classes
        System.out.println("Brand: " + sportsCar.brand);
        System.out.println("Model: " + sportsCar.model);
        System.out.println("Number of doors: " + sportsCar.numberOfDoors);
        sportsCar.move();  // Inherited from Vehicle
        sportsCar.switchGear();  // Inherited from Car
        sportsCar.turboBoost();  // Specific to SportsCar
    }
}

Output:

Brand: Ferrari

Model: 488

Number of doors: 2

The vehicle is moving.

Switching gear.

Activating turbo boost!

• The Vehicle class includes common features like brand, model, and basic movement methods. These elements apply to all types of vehicles.
• A Car class extends a Vehicle and adds specific items, such as the ‘numberOfDoors’ attribute and features like the switchGear() method. It keeps all Vehicle features but adds its own special parts.
• A SportsCar class could extend Car to add high-performance features. Each level adds more specific elements while keeping the base features from the classes above it.

This structure creates clean, organized code. It puts shared features in parent classes and specific features in child classes. This setup makes the code easy to fix and grow over time.

Also Read: What are the Types of Inheritance in Java? Examples and Tips to Master Inheritance

After understanding inheritance in Java and how it builds class hierarchies, it's important to explore polymorphism, which allows for dynamic behavior changes based on the object’s type or context.

What is Polymorphism in Java?

Polymorphism means "many forms" and is a core concept in Java, where objects behave differently based on their context. It allows you to write code that works with objects of a parent class but responds correctly when you use objects of any child class. This creates flexibility in programs and makes code more reusable. 

When discussing differences between inheritance and polymorphism, it’s important to note that inheritance creates a relationship between parent and child classes, enabling code reuse, while polymorphism builds upon this relationship to allow different behaviors depending on the specific object type.

Runtime vs Compile-Time Polymorphism

Polymorphism in Java happens in two ways: at runtime through method overriding and at compile time through method overloading. These mechanisms serve different purposes and work at different stages of program execution.

Method overriding occurs when a child class changes the behavior of a parent class method. The program decides which version of the method to use based on the actual object type when the program runs. Method overloading happens when you create multiple methods with the same name but different parameters. The compiler figures out which method to call based on the parameters you provide.

The table below lists the key distinguishing features between the two types of Polymorphism in Java:

Dynamic Method Dispatch 

Dynamic method dispatch forms the heart of runtime polymorphism in Java. It is a process in Java that helps decide which method to call at runtime. The Java Virtual Machine (JVM) picks the right method version based on the actual object type, not the reference type. When you call a method, Java follows these steps:

• Step 1: It looks at the object's actual type at runtime
• Step 2: It searches for the method in that class
• Step 3: If it does not find the method, it looks in the parent class
• Step 4: This continues up the inheritance chain until it finds the right method

For example:

Animal myPet = new Dog(); 
myPet.makeSound();

Here, even though the reference type is Animal, the program calls Dog's makeSound method. This happens because Java checks the actual object type (Dog) at runtime and uses its method implementation.

Practical Polymorphism Use Cases

Polymorphism helps you create flexible, maintainable code that can handle different types of objects without major changes. Consider a shape-drawing program:

public interface Shape {
    double calculateArea();
    void draw();
}

public class Circle implements Shape {
    private double radius;

    // Constructor to initialize radius
    public Circle(double radius) {
        this.radius = radius;
    }

    @Override
    public double calculateArea() {
        return Math.PI * radius * radius;
    }

    @Override
    public void draw() {
        System.out.println("Drawing a circle with radius: " + radius);
    }

    // Main method to test
    public static void main(String[] args) {
        // Creating a Circle object
        Circle circle = new Circle(5.0);

        // Calling the methods
        System.out.println("Area of circle: " + circle.calculateArea());
        circle.draw();
    }
}

Output:

Area of circle: 78.53981633974483

Drawing a circle with radius: 5.0

Here, this structure shows interface-driven flexibility and provides several benefits:

• You can treat all shapes the same way through the Shape interface
• Each shape implements its own drawing and area calculation logic
• You can add new shapes without changing existing code
• The program can work with a collection of different shapes uniformly

This can be applied to a real application to:

• Draw different shapes on a canvas
• Calculate the total area of mixed shapes
• Save shapes to a file
• Apply transformations to any shape

This approach makes the code more maintainable and easier to extend with new features

Also Read: Understanding the Difference Between Abstraction and Encapsulation

Having explored polymorphism in Java, let’s look at how to determine the right time to use Inheritance vs Polymorphism to create structured and flexible code.

When to Use Inheritance vs Polymorphism in Java?

The differences between inheritance and polymorphism determine how your program evolves. Each approach serves a unique purpose and fits specific situations. Understanding when to use each helps in designing more efficient programs. Inheritance establishes class hierarchies, while polymorphism enables flexible behaviors that adapt to different contexts. Let’s dive into their use cases in detail.

When to Choose Inheritance?

Use inheritance when there is a clear parent-child relationship between classes. It works well when many classes share common features, like animals needing eating and sleeping methods. For example, a Bird class can inherit from Animal and add specific features like flying. Inheritance is great for:

• Building on shared functionality
• Creating systems with clear hierarchies
• Reducing code duplication

When Polymorphism Shines?

Polymorphism is ideal when different objects need to behave in different ways. It allows objects to respond to the same method differently depending on their type. Use polymorphism when:

• You need flexibility, like in plugin architectures that add new features dynamically
• You want to decouple code and make systems easier to maintain
• You need dynamic behavior changes during runtime, like adjusting actions based on conditions

In short, inheritance is best for shared structures, and polymorphism excels when behavior needs to vary.

Combining Inheritance and Polymorphismin Java

Despite the difference between inheritance and Polymorphism, they work together to create flexible, organized code. Here is how you can combine them effectively:

Step 1: Start with inheritance to build your class structure:

• Create a base class with common features
• Add specific features in child classes
• Use abstract classes for shared implementation

Step 2: Add polymorphic behavior:

• Override methods where child classes need different behavior
• Create interfaces for flexible interactions
• Use abstract methods to enforce implementation

Consider the sample code for combining

// Abstract class Vehicle
abstract class Vehicle {
    // Abstract method that must be overridden by subclasses
    abstract void move();  

    // Concrete method that can be inherited
    void startEngine() {   
        System.out.println("Starting the engine...");
    }
}

// Car class extending Vehicle
class Car extends Vehicle {
    // Implement the abstract move method for Car
    @Override
    void move() {
        System.out.println("The car is driving.");
    }
}

// Boat class extending Vehicle
class Boat extends Vehicle {
    // Implement the abstract move method for Boat
    @Override
    void move() {
        System.out.println("The boat is sailing.");
    }
}

// Main class to test the code
public class Main {
    public static void main(String[] args) {
        // Creating instances of Car and Boat
        Vehicle myCar = new Car();
        Vehicle myBoat = new Boat();

        // Calling methods
        myCar.startEngine();
        myCar.move();  // Polymorphic behavior, calls Car's move()

        myBoat.startEngine();
        myBoat.move();  // Polymorphic behavior, calls Boat's move()
    }
    }

Output:

Starting the engine...

The car is driving.

Starting the engine...

The boat is sailing.

This combination of Inheritance and Polymorphism in a Java code provides:

• Code reuse through inheritance
• Flexibility through polymorphism
• Clear structure with room to grow
• Easy maintenance and updates

Also Read: OOP vs POP: Difference Between OOP and POP

Having understood the use cases and key differences between inheritance and polymorphism, let’s see how upGrad can help you further your mastery of these concepts in Java.

How Can upGrad Help You Master Inheritance and Polymorphism?

By now, you’ve grasped the key differences between inheritance and polymorphism in Java. Inheritance organizes your classes through parent-child relationships, while polymorphism allows for flexible, context-based behavior changes. Together, they form the foundation of efficient, scalable Java programs.

To apply these concepts and advance your skills, upGrad’s courses offer hands-on projects, personalized mentorship, and practical scenarios to help you grow in your career.

In addition to the specialized courses mentioned above, here are some free foundational courses to help you advance your career in software development.

• Fundamentals of Cloud Computing
• JavaScript Basics from Scratch
• Object-Oriented Principles in Java
• Node JS for Beginners
• Learn Basic Python Programming

If you're unsure where to start, reach out to upGrad’s expert counselors or visit an upGrad offline center to create a learning plan that suits your goals. Take your programming skills to the next level with upGrad!

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Reference:
https://arxiv.org/abs/2503.24299