Question

I got this code from a text book.

 class FirstClass
 {
     int idNo =25;
     public static void print()
     {
         System.out.println("firstclass citizen " + idNo);
     }
 }
 class SecondClass
 {
     int idNo =24;
     public static void print()
     {
         System.out.println("secondclass citizen" + idNo);
     }
 }
 public class People
 {
     //FirstClass female;
     //SecondClass male;
     public static void main(String[] args)
     {
         System.out.println("people from java world");
         FirstClass.print();
         SecondClass.print();
     }
 }

But when compiling this code I got the following errors

People.java:7: error: non-static variable idNo cannot be referenced from a stati
c context
            System.out.println("firstclass citizen " + idNo);
                                                       ^
People.java:16: error: non-static variable idNo cannot be referenced from a stat
ic context
            System.out.println("secondclass citizen" + idNo);
                                                       ^
2 errors

Answer 1

this refer to current Object, you can refer to any member of the current object from within an instance method or a constructor by using this. But you can not use this reference in static context(method or block).

static method can be called without creating object of that class. So if you use this or non-static variable into the static context it will create compilation error.