// null0 DIS
// instance variables as references default to null ref

class Person {
    int k;
    Person a;
    void data() {
	if (a==null)
	    System.out.println("nothing to do");
	else	
	    System.out.println("something to do");
    }
}

public class null0 {
    public static void main(String[] args) {
	
	Person x = new Person();
	x.data();
	x.a = new Person();
	x.data();
    }
    
}

/* output:
nothing to do
something to do
*/