Hierarchical inheritance in Java is a type of inheritance where multiple subclasses inherit from a single superclass. It allows different classes to share common properties and methods defined in the base class while adding their own unique behavior. This creates a tree-like structure that makes code modular, reusable, and easy to maintain.
In this tutorial, we will explain hierarchical inheritance in Java with syntax and examples. You will learn how it works, why Java does not support multiple inheritance, and how concepts like abstraction, encapsulation, and polymorphism fit into this model. We will also cover examples, advantages, and disadvantages to help you understand the practical applications.
Advance your Java programming expertise with our Software Engineering courses and elevate your learning to the next level. Hurry, enroll now.
Hierarchical Inheritance in Java
Hierarchical inheritance is one of the most common and useful types of inheritance in Java. In this, classes inherit properties and behaviors from a single superclass but can have multiple subclasses that inherit from it. This creates a hierarchical relationship among the classes, forming a tree-like structure.
Fast-track your tech career by building future-ready skills in Cloud, DevOps, AI, and Full Stack Development. Get experience, learn from industry experts, and gain the expertise today’s top employers are looking for.
The Syntax of Java Inheritance
In Java, inheritance is implemented using the extends keyword. The syntax for creating a subclass that inherits from a superclass is as follows:
class Subclass extends Superclass {
}We need to familiarize ourselves with two main syntaxes when working with inheritance in Java.
- Subclass: The name of the subclass you want to create.
- Superclass: The name of the superclass that the subclass is inheriting from.
Now, let us look at an example to understand hierarchical inheritance in Java. Suppose we have a superclass called Vehicle, which represents generic properties and behaviors of vehicles. It can have subclasses like Car, Motorcycle, and Truck, which inherit from it.
The Vehicle class can have common attributes and methods that apply to all types of vehicles, such as color, speed, start(), and stop(). Each subclass (Car, Motorcycle, and Truck) can also have its own specific attributes and methods.
Here is an example:
Code for main.java file:
public class Main {
public static void main(String[] args) {
Car car = new Car();
car.color = "Red";
car.speed = 60;
car.numberOfDoors = 4;
car.start();
car.drive();
car.stop();
System.out.println("-----");
Motorcycle motorcycle = new Motorcycle();
motorcycle.color = "Black";
motorcycle.speed = 100;
motorcycle.hasSidecar = false;
motorcycle.start();
motorcycle.wheelie();
motorcycle.stop();
System.out.println("-----");
Truck truck = new Truck();
truck.color = "Blue";
truck.speed = 40;
truck.cargoCapacity = 5000;
truck.start();
truck.load();
truck.unload();
truck.stop();
}
}
Code for vehicle.java file:
class Vehicle {
String color;
int speed;
void start() {
System.out.println("Vehicle started.");
}
void stop() {
System.out.println("Vehicle stopped.");
}
}
class Car extends Vehicle {
int numberOfDoors;
void drive() {
System.out.println("Car is being driven.");
}
}
class Motorcycle extends Vehicle {
boolean hasSidecar;
void wheelie() {
System.out.println("Performing a wheelie.");
}
}
class Truck extends Vehicle {
int cargoCapacity;
void load() {
System.out.println("Truck is being loaded.");
}
void unload() {
System.out.println("Truck is being unloaded.");
}
}
In this example, we create instances of the Car, Motorcycle, and Truck classes, set their attributes, and invoke their methods. The program outputs the corresponding messages to demonstrate the behavior of each class.
We can see how the subclasses Car, Motorcycle, and Truck inherit properties and methods from the Vehicle superclass. Each subclass also introduces its own unique attributes and methods, demonstrating the concept of hierarchical inheritance in Java.
Must Read: Set in Java: Operations, Examples & Uses
Abstraction
Let us look at an example where we will achieve abstraction by defining an abstract superclass MediaPlayer that hides the implementation details of playing media and exposes only the essential methods (play(), stop()) and the abstract method displayMediaDetails().
The subclasses AudioPlayer and VideoPlayer inherit the common functionality from MediaPlayer and provide concrete implementations for displaying the details specific to audio and video media.
abstract class MediaPlayer {
private boolean isPlaying;
public void play() {
isPlaying = true;
System.out.println("Playing media...");
}
public void stop() {
isPlaying = false;
System.out.println("Stopped media.");
}
public abstract void displayMediaDetails();
}
class AudioPlayer extends MediaPlayer {
private String songTitle;
public AudioPlayer(String songTitle) {
this.songTitle = songTitle;
}
public void displayMediaDetails() {
System.out.println("Playing audio: " + songTitle);
}
}
class VideoPlayer extends MediaPlayer {
private String videoTitle;
public VideoPlayer(String videoTitle) {
this.videoTitle = videoTitle;
}
public void displayMediaDetails() {
System.out.println("Playing video: " + videoTitle);
}
}
public class Main {
public static void main(String[] args) {
AudioPlayer audioPlayer = new AudioPlayer("Song 1");
audioPlayer.play();
audioPlayer.displayMediaDetails();
audioPlayer.stop();
VideoPlayer videoPlayer = new VideoPlayer("Video 1");
videoPlayer.play();
videoPlayer.displayMediaDetails();
videoPlayer.stop();
}
}In this example, MediaPlayer is an abstract class because it contains at least one abstract method (displayMediaDetails()) and cannot be instantiated directly. It defines common functionality for playing media and maintains a state (isPlaying) to track whether the media is being played or stopped.
Now, in the AudioPlayer subclass, we define a specific attribute songTitle and implement the displayMediaDetails() method to display the details of the currently playing audio. Similarly, in the VideoPlayer subclass, we define an attribute videoTitle and implement the displayMediaDetails() method to display the details of the currently playing video.
Read to Learn More: Abstraction in Java: Types of Abstraction Explained Examples
Encapsulation
Now that we have learned about abstraction let us see an example of inheritance in Java that demonstrates encapsulation and hierarchical inheritance:
Code for main.java file:
public class Main {
public static void main(String[] args) {
Dog dog = new Dog("Buddy");
dog.eat();
dog.bark();
Cat cat = new Cat("Whiskers");
cat.eat();
cat.meow();
}
}
Code for animal.java file:
class Animal {
private String name;
public Animal(String name) {
this.name = name;
}
public void eat() {
System.out.println(name + " is eating.");
}
public String getName() {
return name;
}
}
class Dog extends Animal {
public Dog(String name) {
super(name);
}
public void bark() {
System.out.println(getName() + " is barking.");
}
}
class Cat extends Animal {
public Cat(String name) {
super(name);
}
public void meow() {
System.out.println(getName() + " is meowing.");
}
}Must Read: Encapsulation in Java with Example
Polymorphism
Polymorphism fundamentally allows objects from different classes to be treated like objects of common superclasses. In the case of hierarchical inheritance, multiple subclasses inherit from a single superclass, which creates a hierarchical relationship among the classes.
Here's a hierarchical inheritance example that explores polymorphism in Java:
Code for main.java file:
public class Main {
public static void main(String[] args) {
Animal animal1 = new Dog();
Animal animal2 = new Cat();
Animal animal3 = new Cow();
animal1.makeSound();
animal2.makeSound();
animal3.makeSound();
}
}
Code for animal.java file:
class Animal {
public void makeSound() {
System.out.println("The animal makes a sound");
}
}
class Dog extends Animal {
@Override
public void makeSound() {
System.out.println("The dog barks");
}
}
class Cat extends Animal {
@Override
public void makeSound() {
System.out.println("The cat meows");
}
}
class Cow extends Animal {
@Override
public void makeSound() {
System.out.println("The cow moos");
}
}Must Read: Polymorphism in Java: Concepts, Types, Characterisitics & Examples
Why Multiple Inheritance Is Not Supported in Java?
Multiple inheritance in Java is not supported; it's like asking a creature to be physically present in two places at once, which violates the laws of nature.
Just like a person can have only one biological set of parents, a Java class can have only one direct superclass. Multiple inheritances can lead to conflicts and confusion when two superclasses define methods or variables with the same name.
Java avoids this complexity and opts for a simpler, more organized single inheritance model. So, in the case of Java, classes choose their superclasses wisely, embracing the elegance of simplicity over the perplexities of duality.
Real-World Example of Hierarchical Inheritance in Java
Here is a real-world example of hierarchical inheritance in Java:
class Shape {
public void draw() {
System.out.println("Drawing a shape");
}
}
class Rectangle extends Shape {
@Override
public void draw() {
System.out.println("Drawing a rectangle");
}
}
class Circle extends Shape {
@Override
public void draw() {
System.out.println("Drawing a circle");
}
}
public class Main {
public static void main(String[] args) {
Shape shape1 = new Rectangle();
Shape shape2 = new Circle();
shape1.draw();
shape2.draw();
}
}Also Read: String Array In Java: Java String Array With Coding Examples
Advantages of Inheritance in Java
Inheritance provides several advantages in Java. Here are some key advantages:
- Code Reusability: Inheritance allows the user to create a new class by inheriting the properties and methods of an existing class. This promotes code reusability.
- Modularity and Extensibility: Inheritance promotes modular programming. This allows the user to divide the code into logical and hierarchical structures. The user can create a base class with common attributes and behaviors and derive specialized classes from it. This enables the user to extend the functionality of the base class.
- Polymorphism: Inheritance is closely tied to polymorphism. It is a powerful concept in object-oriented programming. Polymorphism allows objects from different classes to be treated as objects from a common superclass. You can create a collection of objects of different derived classes using inheritance.
- Method Overriding: Inheritance enables method overriding. This allows a derived class to provide a different implementation for a method defined in the base class. This feature is crucial for achieving runtime polymorphism.
- Code Organization and Maintenance: Inheritance promotes better code organization. This is maintained by creating a hierarchical structure of classes. This makes it easier to understand and manage the codebase. This happens especially in large-scale projects.
- Encapsulation and Abstraction: Inheritance helps achieve encapsulation and abstraction. You encapsulate related data and behaviors in a single entity by defining a base class with common attributes and methods. Derived classes inherit this encapsulated state and behavior.
Must Read: For Loop Program in Java: Syntax and Examples
Disadvantages of Inheritance in Java
While inheritance provides several advantages in Java, it also has some potential disadvantages that should be considered. Here are a few disadvantages of using inheritance:
- Tight Coupling: Inheritance can lead to tight coupling between classes, especially in deep inheritance hierarchies. This tight coupling can make the code more fragile and difficult to maintain.
- Inheritance Hierarchy Complexity: As the inheritance hierarchy grows larger and deeper, it may become challenging to trace the flow of execution and determine the origin of specific behaviors or properties. Overuse of inheritance can result in a convoluted design.
- Inflexibility: Inheritance establishes a rigid relationship between the base and derived classes. This lack of flexibility can limit the ability to adapt to changing requirements or reuse code in different contexts.
- Method Overriding Issues: If the base class changes its method implementation, all derived classes using method overriding will inherit the new behavior. This can lead to unexpected results if the derived classes were designed to rely on the previous implementation.
- Increased Complexity in Understanding Code Flow: In large inheritance hierarchies, it can be challenging to understand the flow of execution. This can make the code harder to debug and maintain.
- Name Clashes and Diamond Problem: Inheritance can lead to name clashes. This happens when two or more parent classes define methods or properties with the same name. This ambiguity can create conflicts and make the code more error-prone.
Conclusion
Hierarchical inheritance in Java is a powerful concept that allows multiple subclasses to share the features of a single superclass. It improves code reusability, promotes modular design, and supports concepts like polymorphism, abstraction, and encapsulation. By organizing classes into a tree-like structure, it simplifies development and reduces redundancy.
However, developers must also be cautious of tight coupling and complexity in large hierarchies. Understanding hierarchical inheritance in Java with examples is essential for building scalable, maintainable applications. Mastering this concept provides a solid foundation for working with object-oriented programming in real-world Java projects.
FAQs
1. Can constructors be inherited in hierarchical inheritance in Java?
No, constructors are not inherited in hierarchical inheritance in Java. Each subclass must define its own constructor, but it can call the constructor of the superclass using the super keyword. This ensures proper initialization of superclass properties before executing the subclass’s specific code.
2. What is method overriding in hierarchical inheritance?
Method overriding in hierarchical inheritance allows a subclass to redefine a method already present in the superclass. In Java, the subclass method must have the same name, parameters, and return type. This enables polymorphism, allowing different subclasses to provide their own behavior while maintaining a common interface through the superclass.
3. Can a subclass access private members of the superclass in Java inheritance?
No, a subclass in hierarchical inheritance cannot directly access private members of its superclass. Private fields and methods are restricted to the class in which they are defined. However, subclasses can access them indirectly through protected or public getters and setters defined in the superclass.
4. What is hierarchical inheritance in Java?
Hierarchical inheritance in Java is when multiple subclasses inherit from a single superclass. This creates a tree-like structure where the superclass defines common attributes and methods, while subclasses extend it with their own specialized behavior. For example, a superclass Vehicle can have subclasses like Car, Bike, and Truck.
5. How does hierarchical inheritance differ from multiple inheritance in Java?
Hierarchical inheritance involves multiple subclasses extending a single superclass, while multiple inheritance allows a subclass to inherit from more than one superclass. Java does not support multiple inheritance with classes to avoid conflicts, but it supports hierarchical inheritance. This ensures cleaner code and eliminates ambiguity.
6. Why is hierarchical inheritance commonly used in Java?
Hierarchical inheritance is commonly used in Java because it promotes code reusability and better organization. A single superclass defines common properties, and multiple subclasses extend those functionalities. This reduces redundancy, makes the code easier to maintain, and supports object-oriented principles like polymorphism and abstraction.
7. Can we implement hierarchical inheritance using interfaces in Java?
Yes, hierarchical inheritance can be implemented using interfaces in Java. Multiple classes can implement the same interface, which acts like a common contract. However, unlike classes, interfaces only define method signatures, and subclasses must provide the actual implementations.
8. What are the real-world examples of hierarchical inheritance in Java?
A common real-world example of hierarchical inheritance in Java is a superclass Shape with subclasses Circle, Rectangle, and Triangle. Each subclass inherits methods like draw() from Shape but overrides it to implement shape-specific drawing behavior. This demonstrates code reusability and polymorphism.
9. How does polymorphism work in hierarchical inheritance?
Polymorphism in hierarchical inheritance allows objects of different subclasses to be treated as objects of a common superclass. For instance, if Dog and Cat inherit from Animal, an Animal reference can store either a Dog or a Cat object, and the overridden makeSound() method will execute based on the actual object type.
10. What are the advantages of hierarchical inheritance in Java?
Hierarchical inheritance provides advantages like code reusability, modularity, better organization, polymorphism, and easier maintenance. By placing common code in a superclass, developers reduce duplication. Subclasses extend this functionality, making the design more flexible and extensible.
11. What are the disadvantages of hierarchical inheritance in Java?
The disadvantages include tight coupling between classes, difficulty in maintaining deep inheritance hierarchies, reduced flexibility due to rigid superclass-subclass relationships, and complexity when debugging large projects. Overuse of inheritance can also make the design harder to understand.
12. Can abstract classes be used in hierarchical inheritance in Java?
Yes, abstract classes are often used in hierarchical inheritance in Java. An abstract class defines common attributes and methods, including abstract methods that must be implemented by subclasses. This ensures consistency across multiple subclasses while promoting abstraction.
13. How do we achieve encapsulation in hierarchical inheritance?
Encapsulation in hierarchical inheritance is achieved by declaring class variables as private and accessing them through getters and setters. The superclass can encapsulate common data, while subclasses extend functionality without directly exposing sensitive variables. This protects data integrity.
14. Why is multiple inheritance not supported in Java?
Java does not support multiple inheritance with classes to avoid the diamond problem, where ambiguity arises if two parent classes define the same method. Instead, Java allows multiple inheritance through interfaces, ensuring clarity while still offering flexibility.
15. What is the difference between hierarchical inheritance and multilevel inheritance?
Hierarchical inheritance involves one superclass and multiple subclasses, whereas multilevel inheritance is when a subclass acts as a superclass for another subclass, forming a chain. For example, Animal → Mammal → Dog is multilevel, while Animal → Dog and Animal → Cat is hierarchical.
16. Can hierarchical inheritance be combined with multilevel inheritance?
Yes, hierarchical inheritance can be combined with multilevel inheritance. For example, Animal can be a superclass with Dog and Cat as subclasses. Dog may further have a subclass Puppy, making the inheritance structure both hierarchical and multilevel.
17. What is the role of the super keyword in hierarchical inheritance?
The super keyword in hierarchical inheritance is used by subclasses to call constructors and methods of the superclass. This ensures that the superclass’s attributes are properly initialized before executing subclass-specific behavior.
18. How does method overloading differ from method overriding in hierarchical inheritance?
Method overloading occurs when multiple methods in a class share the same name but have different parameter lists. Method overriding happens when a subclass provides a new implementation for a method defined in the superclass. In hierarchical inheritance, overriding supports runtime polymorphism, while overloading enhances flexibility.
19. Is hierarchical inheritance possible with interfaces in Java?
Yes, hierarchical inheritance is possible with interfaces. Multiple classes can implement the same interface, inheriting its method contracts. Additionally, interfaces themselves can extend other interfaces, allowing hierarchical relationships.
20. What is the best use case of hierarchical inheritance in Java?
The best use case of hierarchical inheritance in Java is when multiple entities share common attributes but also require specialized behavior. For example, in a banking system, Account can be a superclass, and subclasses like SavingsAccount, CurrentAccount, and LoanAccount can extend it with specific rules.
Take the Free Quiz on Java
Answer quick questions and assess your Java knowledge
-9cd0a42cab014b9e8d6d4c4ba3f27ab1.webp&w=3840&q=75)
