Lecture_7-Encapsulation in Java.pptx

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1. Lecture – 7 Encapsulation in Java Lecturer Department of CSE Daffodil International University

2. Contents Encapsulation in Java How to implement encapsulation Advantage of Encapsulation Useful Links ‹#›

3. Topic : Encapsulation in Java ‹#›

4. Introduction to Encapsulation Encapsulation is one of the four fundamental OOP concepts . The other three are inheritance , polymorphism , and abstraction . It is the process of binding data and the corresponding methods under a single unit . It is the process of hiding information details and protecting data and behavior of the object. In encapsulation , the variables of a class will be hidden from other classes , and can be accessed only through the methods of their current class. Therefore, it is also known as data hiding. ‹#›

5. To achieve this, you must: 1. declare class variables/attributes as private 2. provide public get and set methods to access and update the value of a private variable How to implement encapsulation ‹#›

6. We know, private variables can only be accessed within the same class (an outside class has no access to it). However, it is possible to access them if we provide public get and set methods . The get method returns the variable value , and the set method sets the value . Syntax for both is that they start with either get or set , followed by the name of the variable , with the first letter in upper case : e.g. If the name of the variable is studntID , then the methods names will be getStudentId() and setStudentId(). Get and Set Methods ‹#›

7. public class Person { private String name ; // private = restricted access // Setter Method public void setName (String newName) { this.name = newName; } // Getter Method public String getName() { return name; } } Example – 1 ‹#›

8. The set method takes a parameter ( newName ) and assigns it to the name variable . The ‘ this’ keyword is used to refer to the current object. The get method returns the value of the name variable. However, as the name variable is declared as private , we cannot access it from outside this class Example - 1 explained ‹#›

9. As the name variable is declared as private , we cannot access it from outside this class public class Person { private String name ; // private = restricted access // Setter public void setName (String newName) { this.name = newName; } // Getter public String getName() { return name; } } Example – 1 ( Error ) ‹#› public class Main { public static void main ( String [] args ) { Person myObj = new Person (); myObj . name = "John" ; // error System . out . println ( myObj . name ); // error } }

10. We can access the private variables with setter and getter methods of that calss. public class Person { private String name ; // private = restricted access // Setter public void setName (String newName) { this.name = newName; } // Getter public String getName() { return name; } } Example – 1 ‹#› public class Main { public static void main ( String [] args ) { Person myObj = new Person (); myObj . setName ( "John" ); // Set the value of the name variable to “John" System . out . println ( myObj . getName ()); } } // Outputs "John"

11. public class Person { private String name; private int age; public void setName(String name) { this.name = name; } public void setAge(int age) { this.age = age; } public String getName() { return name; } public int getAge() { return age; } } Example – 2 ‹#› public class EncapsulaionExample { public static void main(String[] args) { Person p1 = new Person(); p1.setName("Asha"); p1.setAge(20); System.out.println("Name: "+p1.getName()); System.out.println("Age: "+p1.getAge()); } } // Outputs Name: Asha Age: 20

12. UML representation of Example – 2 ‹#› Person - name: String - age: int +Person(String, int) +setName(String) : void +setId(int) : void +getName(): String +getId():int MyClass +main(String [] ) : void

13. ‹#› Check Balance Update Balance ATM GUI Data Hiding: By declaring variables as private, we can achieve data hiding. we cannot access it from outside this class Abstraction : Highlighting the service that are offering without explaining internal design/information is the concept of Abstraction. Using ATM Card, We just swipe the card Enter the password Do the transaction We don’t know the internal procedure. Being the end user we just need to knowhow to use the card. [Encapsulation = Data Hiding + Abstraction]

14. public class Account { private double balance ; // data hiding public double getBalance () { //Validation return balance; } public void setBalance (double balance) { //Validation this.balance = balance; } } Example – 2 [Encapsulation = Data Hiding + Abstraction] ‹#› Check Balance Update Balance ATM GUI

15. Example – 3.1 ‹#› Student - name: String - id: int - cgpa : double +setName(String) : void +setId(int) : void +setCgpa(double): void +getName():String +getId(): int +getCgpa () : double MyClass +main(String [] ) : void

16. Example – 3.2 ‹#› Student - name: String - id: int - cgpa : double +Student(String, int, double) +setName(String) : void +setId(int) : void +setCgpa(double): void +getName():String +getId(): int +getCgpa () : double MyClass +main(String [] ) : void

17. Example – 4 ‹#› Employee - name: String - id: int - salary : double +Employee(String, int, double) +setName(String) : void +setId(int) : void +setSalary(double): void +getName():String +getId(): int +getSalary() : double MyClass +main(String [] ) : void

18. Data Hiding: It is a way to achieve  data hiding  in Java because other class will not be able to access the data through the private data members . It increases the security of data Increased Flexibility: By providing only a setter or getter method, you can make the class  read-only or write-only depending on our requirement. Reusability: Encapsulation also improves the re-usability and is easy to change with new requirements. The programmer can change one part of the code without affecting other parts. Testing code is easy: Encapsulated code is easy to test for unit testing. Advantage of Encapsulation ‹#›

19. https://www.tutorialspoint.com/java/java_encapsulation.htm https://beginnersbook.com/2013/05/encapsulation-in-java/ https://www.javatpoint.com/encapsulation https://techvidvan.com/tutorials/java-encapsulation/ Video Tutorial: https://www.youtube.com/watch?v=QFl9HhrpRFA https://www.youtube.com/watch?v=cU94So54cr8 ‹#› Some helpful Links

20. Thank you! ‹#›