Java - OOPs (Object-Oriented Programming) Concepts

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OOPs (Object-Oriented Programming System)

Object means a real-world entity such as a mobile, book, table, computer, watch, etc. Object-Oriented Programming is a methodology or paradigm to design a program using classes and objects. It simplifies software development and maintenance by providing some concepts.

In this tutorial, we will learn about the concepts of Java (OOPs) object-oriented programming systems.

Java OOPs (Object-Oriented Programming) Concepts

• Class
• Object
• Inheritance
• Polymorphism
• Abstraction
• Encapsulation

Class

In object-oriented programming, a class is a blueprint from which individual objects are created (or, we can say a class is a data type of an object type). In Java, everything is related to classes and objects. Each class has its methods and attributes that can be accessed and manipulated through the objects.

Examples of Class

If you want to create a class for students. In that case, "Student" will be a class, and student records (like student1, student2, etc) will be objects.

We can also consider that class is a factory (user-defined blueprint) to produce objects.

// create a Student class
public class Student {
   // Declaring attributes
   String name;
   int rollNo;
   String section;

   // initialize attributes
   Student(String name, int rollNo, String section){
      this.name= name;
      this.rollNo = rollNo;
      this.section = section;
   }
   // print details	  
   public void printDetails() {
      System.out.println("Student Details:");
      System.out.println(this.name+ ", "+", " + this.rollNo + ", " + section);
   }
}

Object

In object-oriented programming, an object is an entity that has two characteristics (states and behavior). Some of the real-world objects are book, mobile, table, computer, etc. An object is a variable of the type class, it is a basic component of an object-oriented programming system. A class has the methods and data members (attributes), these methods and data members are accessed through an object. Thus, an object is an instance of a class.

Example of Objects

Continuing with the example of students, let's create some students as objects and print their details.

// create a Student class
public class Student {
   // Declaring attributes
   String name;
   int rollNo;
   String section;

   // initialize attributes
   Student(String name, int rollNo, String section){
      this.name= name;
      this.rollNo = rollNo;
      this.section = section;
   }
   // print details	  
   public void printDetails() {
      System.out.print("Student Details: ");
      System.out.println(this.name+ ", " + this.rollNo + ", " + section);
   }

   public static void main(String[] args) {
      // create student objects  
      Student student1 = new Student("Robert", 1, "IX Blue");
      Student student2 = new Student("Adam", 2, "IX Red");
      Student student3 = new Student("Julie", 3, "IX Blue");

      // print student details
      student1.printDetails();
      student2.printDetails();
      student3.printDetails();
   }
}

Output

Let us compile and run the above program, this will produce the following result −

Student Details: Robert, 1, IX Blue
Student Details: Adam, 2, IX Red
Student Details: Julie, 3, IX Blue

Inheritance

In object-oriented programming, inheritance is a process by which we can reuse the functionalities of existing classes to new classes. In the concept of inheritance, there are two terms base (parent) class and derived (child) class. When a class is inherited from another class (base class), it (derived class) obtains all the properties and behaviors of the base class.

Example of Inheritance

Continuing with the example of students, let's make student a derived class of person class. Person class will have a single field name and student class will inherit the same as shown below:

// base class for all students
class Person {
   String name;

   Person(String name){
      this.name = name;
   }
}

// create a Student class
public class Student extends Person {
   // Declaring attributes
   int rollNo;
   String section;

   // initialize attributes
   Student(String name, int rollNo, String section){
      super(name);
      this.rollNo = rollNo;
      this.section = section;
   }
   // print details	  
   public void printDetails() {
      System.out.print("Student Details: ");
      System.out.println(this.name+ ", " + this.rollNo + ", " + section);
   }

   public static void main(String[] args) {
      // create student objects  
      Student student1 = new Student("Robert", 1, "IX Blue");
      Student student2 = new Student("Adam", 2, "IX Red");
      Student student3 = new Student("Julie", 3, "IX Blue");

      // print student details
      student1.printDetails();
      student2.printDetails();
      student3.printDetails();
   }
}

Output

Let us compile and run the above program, this will produce the following result −

Student Details: Robert, 1, IX Blue
Student Details: Adam, 2, IX Red
Student Details: Julie, 3, IX Blue

Polymorphism

The term "polymorphism" means "many forms". In object-oriented programming, polymorphism is useful when you want to create multiple forms with the same name of a single entity. To implement polymorphism in Java, we use two concepts method overloading and method overriding.

The method overloading is performed in the same class where we have multiple methods with the same name but different parameters, whereas, the method overriding is performed by using the inheritance where we can have multiple methods with the same name in parent and child classes.

Example of Polymorphism

Continuing with the example of students, let's add another method printDetails() with additional parameter to modify the behavior of the method.

// create a Student class
public class Student {
   // Declaring attributes
   String name;
   int rollNo;
   String section;

   // initialize attributes
   Student(String name, int rollNo, String section){
      this.name= name;
      this.rollNo = rollNo;
      this.section = section;
   }
   // print details	  
   public void printDetails() {
      System.out.print("Student Details: ");
      System.out.println(this.name+ ", " + this.rollNo + ", " + section);
   }

   // print details without section if required	  
   public void printDetails(boolean hideSection) {
      System.out.print("Student Details: ");
      System.out.println(this.name+ ", " + this.rollNo + ", " + (hideSection ? "" : section));
   }

   public static void main(String[] args) {
      // create student objects  
      Student student1 = new Student("Robert", 1, "IX Blue");
      Student student2 = new Student("Adam", 2, "IX Red");
      Student student3 = new Student("Julie", 3, "IX Blue");

      // print student details
      student1.printDetails();
      student2.printDetails(true);
      student3.printDetails(false);
   }
}

Output

Let us compile and run the above program, this will produce the following result −

Student Details: Robert, 1, IX Blue
Student Details: Adam, 2, 
Student Details: Julie, 3, IX Blue

Abstraction

In object-oriented programming, an abstraction is a technique of hiding internal details and showing functionalities. The abstract classes and interfaces are used to achieve abstraction in Java.

The real-world example of an abstraction is a Car, the internal details such as the engine, process of starting a car, process of shifting gears, etc. are hidden from the user, and features such as the start button, gears, display, break, etc are given to the user. When we perform any action on these features, the internal process works.

Example of Abstraction

Let's create an Abstract Vehicle class and Car extending the Vehicle class. Vehicle will abstract away internal functionalities.

abstract class Vehicle {
   public void startEngine() {
      System.out.println("Engine Started");
   }
}
public class Car extends Vehicle {
   private String color;

   public Car(String color) {
      this.color = color;
   }

   public void printDetails() {
      System.out.println("Car color: " + this.color);
   }

   public static void main(String[] args) {
      Car car = new Car("White");

      car.printDetails();
      car.startEngine();
   }
}

Output

Let us compile and run the above program, this will produce the following result −

Car color: White
Engine Started

Encapsulation

In an object-oriented approach, encapsulation is a process of binding the data members (attributes) and methods together. The encapsulation restricts direct access to important data. The best example of the encapsulation concept is making a class where the data members are private and methods are public to access through an object. In this case, only methods can access those private data.

Example of Objects

Continuing with the example of students, let's create some students as objects and print their details.

// create a Student class
public class Student {
   // Declaring private attributes
   private String name;
   private int rollNo;
   private String section;

   // initialize attributes
   Student(String name, int rollNo, String section){
      this.name= name;
      this.rollNo = rollNo;
      this.section = section;
   }
   // print details	  
   public void printDetails() {
      System.out.print("Student Details: ");
      System.out.println(this.name+ ", " + this.rollNo + ", " + section);
   }

   public static void main(String[] args) {
      // create student objects  
      Student student1 = new Student("Robert", 1, "IX Blue");
      Student student2 = new Student("Adam", 2, "IX Red");
      Student student3 = new Student("Julie", 3, "IX Blue");

      // print student details
      student1.printDetails();
      student2.printDetails();
      student3.printDetails();
   }
}

Output

Let us compile and run the above program, this will produce the following result −

Student Details: Robert, 1, IX Blue
Student Details: Adam, 2, IX Red
Student Details: Julie, 3, IX Blue

Advantages of Java OOPs

The following are the advantages of using the OOPs in Java:

• The implementations of OOPs concepts are easier.
• The execution of the OOPs is faster than procedural-oriented programming.
• OOPs provide code reusability so that a programmer can reuse an existing code.
• OOPs help us to keep the important data hidden.