Module 2: Object Oriented Programming

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.
  • 
• 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
  • In hybrid inheritance, a class can inherit the properties of more than one class and one interface.
  • In Java, hybrid inheritance is achieved by extending a class and implementing an interface.
  • 

Polymorphism

Overriding/Overloading

Image

class A { int a; void displayA() { System.out.println("a = " + a); } }