Module 2: OOPs

OOPs (Objects Oriented Programming)

Encapsulation

• Encapsulation is a process of wrapping up of data under a single unit. It is the mechanism that binds together code and the data its operators.

• In encapsulation, the data is hidden from the user and can be accessed only through the methods of their current class.

• In Java, Java Beans is the best example of encapsulation.

  class Student {
  int studentId;
  String studentName;
  Student(int id, String name) { // parameterized constructor
    studentId = id;
    studentName = name;
  }
  
//  getters and setters
  String getName(){ // getter for studentName
    return studentName;
  }
  int getId(){ // getter for studentId
      return studentId;
  }
  void setName(String name){ // setter for studentName
        studentName = name;
  }
  void setId(int id){ // setter for studentId
        studentId = id;
    }
}

Inheritance

• Inheritance is the process of borrowing the properties of one class to another class
• Inheritance is the best way to achieve code reusability.
• In Java, inheritance is achieved by using the extends keyword.
• The class that inherits the properties of another class is called subclass or child class.

// parent class
class Science {
    // method to know the course
    void knowMyCourse(){
        system.out.println("I am a Science Student");
    }
  
}
// child class
class Student extends Science{
    int studentId;
    String studentName;
    String  studentCourse;
    // constructor
    Student(int id, String name){
        studentId = id;
        studentName = name;
    }    
}
class TestStudent{
    public static void main(String[] args){
        // creating object of child class
        Student s1 = new Student(1, "John");
        // calling method of parent class
        s1.knowMyCourse();
    }
}

There are four types of inheritance in Java:

• Single Inheritance

  • In single inheritance, a class can inherit the properties of only one class.
  • In Java, single inheritance is achieved by extending a class. This is the simplest form of inheritance.

  ---

  

• Multilevel Inheritance

  • In multilevel inheritance, a class can inherit the properties of another class and that class can also inherit the properties of another class.
  • In Java, multilevel inheritance is achieved by extending a class which is already extended by another class.

  

• Hierarchical Inheritance

  • In hierarchical inheritance, a class can inherit the properties of more than one class.
  • In Java, hierarchical inheritance is achieved by extending more than one class.

  

• Hybrid Inheritance

  • Hybrid combination is combination of more than one type of inheritance.
  • In Java, we can combine two inheritance types to achieve hybrid inheritance.

  Note: In Java, multiple inheritance is not supported.

Polymorphism

• The word polymorphism means having many forms.
• Polymorphism is the ability of an object to take on many forms and perform single action in different ways.
• In Java, polymorphism is mainly divided into two types:
  • Compile-time Polymorphism
    • This type of polymorphism is achieved by method overloading.
  • Runtime Polymorphism
    • This type of polymorphism is achieved by method overriding.

class Student{
    int studentId;
    int subjectName;
    void display(){
      System.out.println("I am a student");
    }
}
class Person extends Student{
    String name;
    void display(){
      System.out.println("I am a student and Intern at HotWax Systems");
    }
  }

Overriding/Overloading

• In Java, Polymorphism is mainly divided into two types:
  • Compile-time Polymorphism
    • This type of polymorphism is achieved by method overloading.
    • Method overloading is a feature that allows a class to have more than one method having the same name, if their argument lists are different.
    • These methods are said to be overloaded and differentiated by the compiler by the number of parameters in the list and their types.

    class Addition{
      void add(int a, int b){
        System.out.println(a+b);
      }
      void add(int a, int b, int c){
        System.out.println(a+b+c);
      }

  • Runtime Polymorphism
    • This type of polymorphism is achieved by method overriding.
    • Method overriding is a feature that allows a subclass or child class to provide a specific implementation of a method that is already provided by one of its super-classes or parent classes.

    class Student{
      void display(){
        System.out.println("I am a student");
      }
    }
    class Person extends Student{
      void display(){
        System.out.println("I am a student and Intern at HotWax Systems");
      }
    }