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Java OOP Abstraction - A simple tutorial

by - Techmagister on - 12/24/2018


Abstraction is simply hiding the internal process of a certain class and providing only the final output. This java abstraction tutorial provides a simple yet strong introduction to abstraction in java. Abstraction in java can be divide in to two main categories.

We will discuss about interfaces in another tutorial.

In Abstract classes,


  • Use abstract keyword
  • May contains abstract and none abstract methods
  • Abstract classes cannot be instantiated
  • To use an abstract class, it should be inherited from another class and provide implementations of all abstract methods in it.


Abstract methods

  • Contains abstract keyword
  • Does not contain a method body
  • Ends with semicolon (;)


Consider following code sample.
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public abstract class MyClass { // abstract class
 
 abstract void myMethod(); // abstract method
}

Now, refer following example to get an overall idea about abstraction in java.

This my project hierarchy.

This is Car.java class

  • This is an abstract class, therefore I'm using abstract keyword.
  • It has an abstract method 'createCar' (line 12). In eclipse: press Alt+Shift+S and click on 'generate constructor using fields' to add constructor.
  • Also Car class contains getters and setters for carModel variable. In eclipse: press Alt+Shift+S and click on 'Generate getters and setters' to add those.

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package com.example.abstraction;

public abstract class Car {
 private String carModel;

 public Car(String carModel) {

  this.carModel = carModel;
  System.out.println("Creating a car: " + getCarModel());
 }

 abstract void createCar();

 public String getCarModel() {
  return carModel;
 }

 public void setCarModel(String carModel) {
  this.carModel = carModel;
 }

}

This is Lamborghini.java class

  • Its an inherited class from Car.java class.
  • It has implemented 'createCar' method which is an abstract method in Car.java class (line 11). Also we use 'getCarModel()' to acquire the value for 'carModel' String
  • It has its default constructor (line 5)
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package com.example.abstraction;

public class Lamborghini extends Car {

 public Lamborghini(String carModel) {
  super(carModel);
  // TODO Auto-generated constructor stub
 }

 @Override
 void createCar() {
  System.out.println("Car created: " + getCarModel());
  // TODO Auto-generated method stub

 }

}

This is Main.java class

  • It has main method and instantiated Lamborghini class with Car reference and has passes the 'Lamborghini Avantador' value as 'carModel' string.


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package com.example.abstraction;

public class Main {

 public static void main(String[] args) {
  Car car = new Lamborghini("Lamborghini Avantador");
  car.createCar();

 }
}

When we run the Main.java class. We can have the following output.
Creating a car: Lamborghini Avantador
Car created: Lamborghini Avantador

Now you can understand that abstraction is simply hiding the internal process of a class and showing only the functional output. Getters and setters are used to acquire and set values for fields. This is an introduction to abstraction with a simple but effective example. You can try more complex examples once you have got the idea behind this concept.

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