Create a final class, final reference variable and use it....

import java.util.*;

//This is an example of ImmutableClass

public class ImmutableClassExample{

public static void main (String[] args) {
Employee e1=new Employee("HJPKL6930M");
String s1=e1.getPanCard();
System.out.println("This is your Pan_Card number: "+s1);
}
}
final class Employee{

final String Pan_Card;

Employee(String Pan_Card){
this.Pan_Card=Pan_Card;
}

public String getPanCard(){
return Pan_Card;
}

}