Inheritance is one of the fundamental principles of Object-Oriented Programming (OOP) that allows one class (the child class or subclass) to inherit fields and methods from another class (the parent class or superclass). This promotes code reuse, modularity, and better maintainability.
In this article, we will deep-dive into the concept of multiple inheritance in Java, building upon previous tutorials on inheritance, interface, and composition in Java.
Inheritance in Java is implemented using the extends
keyword. Here’s an example:
// Parent class
class Animal {
void makeSound() {
System.out.println("Animal makes a sound");
}
}
// Child class inheriting from Animal
class Dog extends Animal {
void bark() {
System.out.println("Dog barks");
}
}
public class Main {
public static void main(String[] args) {
Dog dog = new Dog();
dog.makeSound(); // Inherited method
dog.bark(); // Child class method
}
}
This example demonstrates single inheritance, where the Dog
class inherits behavior from the Animal
class.
Java supports different types of inheritance, which define the relationships between classes. These include:
Single Inheritance: A subclass inherits from a single parent class.
For example:
// Parent class
class Animal {
void makeSound() {
System.out.println("Animal makes a sound");
}
}
// Child class inheriting from Animal
class Dog extends Animal {
void bark() {
System.out.println("Dog barks");
}
}
Multilevel Inheritance: A subclass derives from another subclass, forming a hierarchy.
For example:
// Grandparent class
class Animal {
void makeSound() {
System.out.println("Animal makes a sound");
}
}
// Parent class inheriting from Animal
class Mammal extends Animal {
void eat() {
System.out.println("Mammal eats");
}
}
// Child class inheriting from Mammal
class Dog extends Mammal {
void bark() {
System.out.println("Dog barks");
}
}
Hierarchical Inheritance: Multiple classes inherit from the same parent class.
For example:
// Parent class
class Animal {
void makeSound() {
System.out.println("Animal makes a sound");
}
}
// Child class 1 inheriting from Animal
class Dog extends Animal {
void bark() {
System.out.println("Dog barks");
}
}
// Child class 2 inheriting from Animal
class Cat extends Animal {
void meow() {
System.out.println("Cat meows");
}
}
Hybrid Inheritance: A mix of two or more types of inheritance. Java does not support direct hybrid inheritance but can be achieved using interfaces. Here’s an example:
// Interface 1
interface Flyable {
void fly();
}
// Interface 2
interface Walkable {
void walk();
}
// Parent class
class Animal {
void makeSound() {
System.out.println("Animal makes a sound");
}
}
// Child class inheriting from Animal and implementing Flyable and Walkable
class Bird extends Animal implements Flyable, Walkable {
@Override
public void fly() {
System.out.println("Bird flies");
}
@Override
public void walk() {
System.out.println("Bird walks");
}
}
For a deeper dive into OOP concepts in Java, check this tutorial on OOPS Concepts in Java - OOPS Concepts Example.
While inheritance promotes code reuse, it can impact memory usage and performance if not used wisely. Key considerations include:
Memory Consumption: Each subclass instance contains data from both the subclass and superclass, leading to increased memory consumption.
Method Resolution: The JVM must resolve method calls dynamically, which might introduce slight overhead in method lookup.
Deep Inheritance Trees: Excessive inheritance levels can lead to a complex class hierarchy, making debugging and performance tuning difficult.
For performance-critical applications, consider alternatives like composition, which often provides better flexibility and maintainability.
Inheritance in Java is a mechanism where a subclass derives properties and behaviors from a parent class, allowing for code reuse and hierarchical structuring. You can read more about inheritance in this tutorial on Inheritance in Java.
Java supports single, multilevel, hierarchical, and hybrid inheritance. However, multiple inheritance is not supported directly due to the diamond problem.
extends
keyword work in Java?The extends
keyword is used to indicate that a class is inheriting from another class. The child class gains access to the parent class’s methods and fields. Here’s an example:
// Parent class
class Animal {
void makeSound() {
System.out.println("Animal makes a sound");
}
}
// Child class inheriting from Animal
class Dog extends Animal {
void bark() {
System.out.println("Dog barks");
}
}
Inheritance defines a “is-a” relationship, while composition represents a “has-a” relationship. Composition is often preferred for better flexibility. Read more about the differences in this tutorial on Composition vs Inheritance.
Concept | Inheritance | Composition |
---|---|---|
Relationship | “is-a” | “has-a” |
Flexibility | Less flexible | More flexible |
Code Reuse | Promotes code reuse | Promotes code reuse |
Complexity | Can lead to tight coupling | Encourages loose coupling |
Yes, a subclass can override a method from the parent class using the @Override
annotation. This allows the subclass to provide a specific implementation of the inherited method.
Here’s an example:
// Parent class
class Animal {
void makeSound() {
System.out.println("Animal makes a sound");
}
}
// Child class inheriting from Animal
class Dog extends Animal {
@Override
void makeSound() {
System.out.println("Dog makes a sound");
}
}
Java does not support multiple inheritance for classes to prevent ambiguity and diamond problems. This decision was made to ensure that the language remains simple and easy to use, avoiding the complexities that can arise from multiple inheritance. However, multiple inheritance can be achieved using interfaces, which provide a way to implement multiple behaviors without the risks associated with multiple inheritance.
Avoid inheritance when:
Understanding inheritance and its best practices ensures that your Java applications remain efficient, modular, and easy to maintain. By balancing inheritance and composition, you can achieve a well-structured application.
You can learn more about object-oriented programming in this tutorial on OOPS concept in Java.
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Bit confused. “favor composition over interfaces” or “favor composition over inheritance”?.
- Super Hubo
good explanation…
- subbareddy
What is association in Java?
- Madhusmita Nayak
How the multiple inheritance is possible in C , C++ but not in java can u explain the context…
- Elumalai
How the multiple inheritance is possible in C , C++ but not in java can u explain the context…
- Suman
Can u give examples/Complete class defintions to proove your 2nd & 3rd point of Composition better than inheritance.??
- Sorrowfull Blinger
Suppose we have a superclass and subclass as follows: ClassC.java 1 2 3 4 5 6 7 package com.journaldev.inheritance; public class ClassC{ public void methodC(){ } } ClassD.java 1 2 3 4 5 6 7 8 package com.journaldev.inheritance; public class ClassD extends ClassC{ public int test(){ return 0; } } The above code compiles and works fine but what if ClassC implementation is changed like below: ClassC.java 1 2 3 4 5 6 7 8 9 10 package com.journaldev.inheritance; public class ClassC{ public void methodC(){ } public void test(){ } }Suppose we have a superclass and subclass as follows: ClassC.java 1 2 3 4 5 6 7 package com.journaldev.inheritance; public class ClassC{ public void methodC(){ } } ClassD.java 1 2 3 4 5 6 7 8 package com.journaldev.inheritance; public class ClassD extends ClassC{ public int test(){ return 0; } } The above code compiles and works fine but what if ClassC implementation is changed like below: ClassC.java 1 2 3 4 5 6 7 8 9 10 package com.journaldev.inheritance; public class ClassC{ public void methodC(){ } public void test(){ } } I think this not the problem after Jdk 1.5 where we can have different return types for both overriding and overidden methods in the parent and subclass.
- safdar
composition has its limitations. I believe composition is an option as long as the classes and their methods we want to consume are “public”. In case we want to access “protected” members you have to fall back on either Interfaces or Classes. Not denying - composition is a useful means and improves our code refactoring skills.
- Yunus Atheist
There are many advantages of using composition, couple of them are : You will have full control of your implementations. i.e., you can expose only the methods you intend to expose. any changes in the super class can be shielded by modifying only in your class. Any clients classes which uses your classes, need not make modifications. Allows you to control when you want to load the super class (lazy loading)
- Mayank
You are awesome Pankaj.
- Ravi Verma