What is Encapsulation in java - OOPS principles

Encapsulation
In short, encapsulation means data hiding.
To achieve encapsulation >
  • Make fields/memberVariables private (private can be accessed only within the same class, hence we are hiding the fields within the class), and
  • access those private fields via public methods. (Public are accessible from everywhere)


Advantages of using encapsulation >
  • Encapsulation prevents other classes to access the class data (i.e. preventing access to private fields).
  • Encapsulation allows to modify implemented java code without breaking others code who have implemented the code.


  • Outside users who are accessing this class don’t know about the private fields of class,
Example - field may be Integer or  String type, but user won’t have any such information.
So, class at any time can change data type of a field and users won’t know about it, even they need not to. (This point is related to above point)
  • Class fields could be made read-only or write-only.


  • Encapsulation makes our java code>
  • maintainable,
  • extensible and
  • flexible.


Program 1.1 to demonstrate Encapsulation>
class Employee{
   private String id; //private field
   public String getId() { //private field accessed inside public method
          return id;
   }
   public void setId(String id) {
          this.id = id;
   }
  
}
/** JavaMadeSoEasy.com */
public class EncapsulationTest {
   public static void main(String[] args) {
          Employee emp=new Employee();
          emp.setId("1"); //public method can be accessed outside class.
          System.out.println("emp.getId()  >  "+emp.getId());
   }
}
/* OUTPUT
emp.getId()  >  1
*/

What would happen without encapsulation>
No encapsulation means fields won’t be private and could be used outside class.
Program 1.2 - What would happen without encapsulation >
class Employee{
   String id; //No encapsulation - field isn’t private
}
/** JavaMadeSoEasy.com */
public class EncapsulationTest {
   public static void main(String[] args) {
          Employee emp=new Employee();
          emp.id="1";  //As field isn't private, it could be accessed outside class.
         
   }
}

What could be impact of not using encapsulation>
Let’s say data type of id was changed from String to Integer, in that case compilation error will be generated wherever id has been used, because code was written considering id is String not a Integer.
So, by not using encapsulation we will end up breaking others code.
You must be thinking that in below program id has been accessed only at one place, we could make necessary adjustments, but what about id being used at thousands of places in other programs.
Program 1.3 - impact of not using encapsulation

program 1.4 - Now, lets understand how Encapsulation allows to modify implemented java code without breaking others code who have implemented the code via program.


If id would have been private, other classes would have been accessing id outside class only via public methods of class. So, in that case if we were to change data type of id from String to Integer than to avoid breaking of others code we could make relevant changes in setter and getter methods.


In below program >
As compared to other programs data type of id has been changed from String to Integer,and to avoid breaking of others code we make relevant changes in setter and getter methods. ( Please compare setter and getter methods with above program)


class Employee{
   Integer id;
   public String getId() {
          return String.valueOf(id);
   }
   public void setId(String id) {
          this.id = Integer.parseInt(id);
   }
  
}
/** JavaMadeSoEasy.com */
public class EncapsulationTest {
   public static void main(String[] args) {
          Employee emp=new Employee();
          emp.setId("1");
          System.out.println("emp.getId()  >  "+emp.getId());
         
   }
}
/* OUTPUT
emp.getId()  >  1
*/

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