Java Abstract Keyword - Explained with Examples

Unlock the power of the Java abstract keyword with practical examples! This guide empowers developers to grasp abstract classes and methods seamlessly.

Example

An abstract method belongs to an abstract class, and it does not have a body. The body is provided by the subclass:

// Code from filename: Main.java
// abstract class
abstract class Main {
  public String fname = "John";
  public int age = 24;
  public abstract void study(); // abstract method
}

// Subclass (inherit from Main)
class Student extends Main {
  public int graduationYear = 2018;
  public void study() { // the body of the abstract method is provided here
    System.out.println("Studying all day long");
  }
}
// End code from filename: Main.java

// Code from filename: Second.java
class Second {
  public static void main(String[] args) {
    // create an object of the Student class (which inherits attributes and methods from Main)
    Student myObj = new Student();

    System.out.println("Name: " + myObj.fname);
    System.out.println("Age: " + myObj.age);
    System.out.println("Graduation Year: " + myObj.graduationYear);
    myObj.study(); // call abstract method
  }
}

Definition and Usage

The abstract keyword is a non-access modifier, used for classes and methods.

Class: An abstract class is a restricted class that cannot be used to create objects (to access it, it must be inherited from another class).

Method: An abstract method can only be used in an abstract class, and it does not have a body. The body is provided by the subclass (inherited from).

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