10. What is encapsulation in Java ?

The whole idea behind encapsulation is to hide the implementation details from users. 

If a data member is private it means it can only be accessed within the same class. No outside class can access private data member (variable) of other class. However if we setup public getter and setter methods to update (for e.g. void setSSN(int ssn))and read (for e.g.  int getSSN()) the private data fields then the outside class can access those private data fields via public methods. 

This way data can only be accessed by public methods thus making the private fields and their implementation hidden for outside classes. That’s why encapsulation is known as data hiding. Lets see an example to understand this concept better.

public class EncapsulationDemo{

    private int ssn;

    private String empName;

    private int empAge;

    //Getter and Setter methods

    public int getEmpSSN(){

        return ssn;

    }

    public String getEmpName(){

        return empName;

    }

    public int getEmpAge(){

        return empAge;

    }

    public void setEmpAge(int newValue){

        empAge = newValue;

    }

    public void setEmpName(String newValue){

        empName = newValue;

    }

    public void setEmpSSN(int newValue){

        ssn = newValue;

    }

}

public class EncapsTest{

    public static void main(String args[]){

         EncapsulationDemo obj = new EncapsulationDemo();

         obj.setEmpName("Mario");

         obj.setEmpAge(32);

         obj.setEmpSSN(112233);

         System.out.println("Employee Name: " + obj.getEmpName());

         System.out.println("Employee SSN: " + obj.getEmpSSN());

         System.out.println("Employee Age: " + obj.getEmpAge());

    }

}

Output:

Employee Name: Mario

Employee SSN: 112233

Employee Age: 32