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Java Basic

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Java Introduction

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Java Get Started

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Java Syntax

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Java Output / Print

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Java Comments

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Java Variables

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Java Data Types

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Java Type Casting

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Java Operators

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Java Strings

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Java Math

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Java Booleans

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Java If ... Else

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Java Switch

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Java While Loop

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Java For Loop

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Java Break / Continue

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Java Arrays

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Java Methods

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Java Classes

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Java file Handling

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Java How To

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Java Reference

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Java String Methods

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Java Math Methods

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Java Output Methods

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Java Arrays Methods

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Java ArrayList Methods

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Java LinkedList Methods

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Java HashMap Methods

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Java Errors and Exception

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Text lesson

Java Abstraction

Abstract Classes and Methods

Data abstraction involves concealing specific details while presenting only crucial information to the user.
This abstraction can be realized through either abstract classes or interfaces, topics that will be explored further in the upcoming chapter.

The abstract keyword, a non-access modifier, is employed with classes and methods.

  1. An abstract class is a constrained class that cannot be instantiated directly; it requires inheritance from another class for access.
  2. An abstract method is exclusive to an abstract class, devoid of implementation, and relies on the subclass to provide its body through inheritance.

An abstract class is capable of containing both abstract and regular methods.

abstract class Animal {
  public abstract void animalSound();
  public void sleep() {
    System.out.println("Zzz");
  }
}

As illustrated in the example above, creating an object of the Animal class is not feasible.

Animal myObj = new Animal(); // will generate an error

In order to access the abstract class, it must be inherited from another class. Let’s transform the Animal class we utilized in the Polymorphism chapter into an abstract class.

Remember from the Inheritance chapter that we use the extends keyword to inherit from a class.

Example

 // Abstract class
 abstract class Animal {
  // Abstract method (does not have a body)
  public abstract void animalSound();
  // Regular method
  public void sleep() {
    System.out.println("Zzz");
  }
}
  // Subclass (inherit from Animal)
 class Pig extends Animal {
   public void animalSound() {
    // The body of animalSound() is provided here
    System.out.println("The pig says: wee wee");
   }
 }
 class Main {
  public static void main(String[] args) {
    Pig myPig = new Pig(); // Create a Pig object
    myPig.animalSound();
    myPig.sleep();
   }
 }

 

Why And When To Use Abstract Classes and Methods?

For security purposes, abstraction involves concealing specific details and revealing only the essential aspects of an object.

Note: Abstraction can also be accomplished through Interfaces, a concept that will be further explored in the following chapter.

 

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