this problem is actually how constant are initialize and how super interface are called in

JAVA, let me try to explain you :

Suppose you write :

System.out.println(B);

now see how things work:

in case when B is called first values are :

B =2, C =1, A =0

Similarly When

System.out.println(A);

so A =4,B = 2, C = 1

similarly when C is called first :

C =3,A = 2, B =1

so when you call B+C+A

you get : 2 + 1 + 0 = 3

similarly

A + B + C = 4 + 2 + 1 = 7