Abstract Class In Java

An abstract class is a class that cannot be instantiated on its own and is meant to be subclassed. It serves as a blueprint for other classes, providing a common structure that derived classes can implement or override.

Key Characteristics:

Cannot Be Instantiated: You cannot create an instance of an abstract class directly. It must be subclassed, and only the subclasses can be instantiated.
Abstract Methods: An abstract class can have abstract methods, which are declared without an implementation (i.e., no method body). Subclasses must provide implementations for these abstract methods.
Concrete Methods: An abstract class can also have concrete methods with implementations that can be inherited by subclasses.
Instance Variables: Like regular classes, abstract classes can have instance variables.
Constructor: Abstract classes can have constructors, which are called when an instance of a subclass is created.
Access Modifiers: Abstract classes can be declared with access modifiers (public, protected, default).
Polymorphism: Abstract classes are used to achieve polymorphism in Java, allowing a common interface for a group of related classes.

Code Example

​x
 
// Abstract classabstract class Animal {    // Instance variable    private String name;​    // Constructor    public Animal(String name) {        this.name = name;    }​    // Abstract method (no implementation)    public abstract void makeSound();​    // Concrete method (with implementation)    public void eat() {        System.out.println(name + " is eating.");    }​    // Getter for name    public String getName() {        return name;    }}​// Subclass of Animalclass Dog extends Animal {    // Constructor    public Dog(String name) {        super(name);    }​    // Implementing abstract method    @Override    public void makeSound() {        System.out.println(getName() + " says: Woof Woof");    }}​// Subclass of Animalclass Cat extends Animal {    // Constructor    public Cat(String name) {        super(name);    }​    // Implementing abstract method    @Override    public void makeSound() {        System.out.println(getName() + " says: Meow Meow");    }}​// Main class to test the abstract class and its subclassespublic class Main {    public static void main(String[] args) {        // Creating objects of the subclasses        Animal dog = new Dog("Buddy");        Animal cat = new Cat("Whiskers");​        // Calling methods        dog.makeSound();        dog.eat();​        cat.makeSound();        cat.eat();    }}

Output

Buddy says: Woof Woof
Buddy is eating.
Whiskers says: Meow Meow
Whiskers is eating.

Explanation

Abstract Class Animal: This class cannot be instantiated. It has an abstract method makeSound() that must be implemented by any subclass. It also has a concrete method eat() that can be inherited by subclasses.
Subclasses Dog and Cat: These classes extend the Animal class and provide implementations for the abstract method makeSound().
Main Class: In the Main class, we create instances of Dog and Cat, and call their methods to demonstrate the functionality.

Abstract Class in Java

Key Characteristics:

Explanation

Java Tutorial

Python Tutorial