Confusing Java parameter manipulation -

when i'm using a=x, b=y result 15. when i'm using x=a,y=b, result 0. please explain why?

public class test {         int , b;      test(int x, int y) {               a=x;           b=y;      }      int sr() {          return a*b;     }      public static void main (string args[]){          test t=new test(5,3);          system.out.println(t.sr());     }  } 

a=x;  b=y; 

will set instance attributes a & b values passed values x , y. when create instance using :

test t=new test(5,3); 

a , b have values 5 & 3 respectively. hence calling method t.sr return

a*b = 5*3 = 15; 

on other hand if u use:

x = a;  y = b; 

local variables x , y set default values of , b i.e. 0. , b hold defualt values 0 no other value set. when u

 test t=new test(5,3); 

as & b have values 0 calling method t.sr return

a*b = 0*0 = 0;