abstract Keyword in Java

Last Updated : 18 Feb 2026

The Java abstract keyword is a non-access modifier used with classes and methods to achieve abstraction.

Purpose of abstract Keyword

The abstract keyword facilitates abstraction by allowing us to define a blueprint or a contract for classes without providing complete implementation details. It promotes code reusability and enforces a specific structure and behavior for subclasses, ensuring that they implement certain methods.

Characteristics of abstract Keyword

The abstract keyword can be used to declare abstract classes and abstract methods.
We cannot create an object of an abstract class directly. It is meant to be extended by subclasses.
Abstract methods do not have a body (i.e., no implementation). The method ends with a semicolon: abstract void draw();
Abstract classes can implement interfaces, which define a set of methods that must be implemented by any class that implements the interface.
An abstract class can include both abstract methods and concrete (regular) methods with implementations.
Abstract classes can have instance variables, constructors, and even static methods. It can be used by both the abstract class and its subclasses. Subclasses can access these variables directly.
An abstract keyword cannot be used with variables and constructors.
We cannot use the abstract keyword with the final.

Usage of abstract Keyword

The abstract keyword is used to define abstract classes and abstract methods.

Abstract Class

An abstract class is a class that cannot be instantiated (you cannot create objects of it) and may contain abstract methods (methods without a body). For example, java.lang.Number class is an abstract class.

An abstract class can contain constructors and static methods.
An abstract class can contain overloaded abstract methods.
We can declare the local inner class as abstract.
We can declare the abstract method with a throw clause.

To read more Abstract Class in Java

Syntax:

abstract class ClassName {
        // class body
    }
}

Abstract Methods

A method declared using the abstract keyword within an abstract class and does not have a definition (implementation) is called an abstract method. When we need just the method declaration in a super class, it can be achieved by declaring the methods as abstract.

We cannot declare abstract methods as private.
We cannot declare abstract methods as static.
An abstract method can't be synchronized.

To read more Abstract Method in Java

Note: We cannot declare abstract methods in a non-abstract class.

Syntax:

abstract class ClassName {
// Abstract method
    abstract void methodName();  {
        // Method body
    }
}

Example of abstract Keyword

Using abstract Keyword with Class and Method

Example

// Abstract class
abstract class Animal {
    // Abstract method
    abstract void makeSound();
    // Concrete method
    void eat() {
        System.out.println("This animal eats food.");
    }
}
// Subclass providing implementation
class Dog extends Animal {
    @Override
    void makeSound() {
        System.out.println("Dog barks");
    }
}
public class Main {
    public static void main(String[] args) {
        Animal a = new Dog(); // Upcasting
        a.makeSound();        
        a.eat();              
    }
}

Compile and Run

Output:

Dog barks
This animal eats food.

Using Abstract Class with Multiple Subclasses

Example

abstract class Shape {
    abstract void draw();
}
class Circle extends Shape {
    void draw() {
        System.out.println("Drawing Circle");
    }
}
class Square extends Shape {
    void draw() {
        System.out.println("Drawing Square");
    }
}
public class Main {
    public static void main(String[] args) {
        Shape s1 = new Circle();
        Shape s2 = new Square();
        s1.draw(); 
        s2.draw();  
    }
}

Compile and Run

Output:

Drawing Circle
Drawing Square

abstract Keyword Best Practice

Abstract Classes for Shared Code: When shared code is required, use abstract classes so that multiple subclasses can inherit that code.
Mandatory Implementation: Implement all the abstract class methods in subclasses.
Abstract Methods for Interfaces: If we have a class that acts as a base and requires methods to be overridden, use abstract methods to enforce this contract.
Cannot Instantiate: Creating an instance of an abstract class is not allowed directly. So, we must create an instance of a subclass that implements all abstract methods.
Abstract Class Constructors: An abstract class can have constructors, which can be called during the instantiation of a subclass.
Abstract Class with Interface: An interface can be implemented with abstract classes. We can define some methods of interface in the abstract class while leaving others as abstract for implementation in subclasses.
Static Members: An abstract class can have static members that can be accessed without creating an instance of the abstract class.

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