Argument Passing

hi this is my code

class Test {

    void meth(int i, int j) {
        i *= 2;
        j /= 2;
        System.out.println("a=" +i);
        System.out.println("b=" +j);
    }
}
public class CallByValue1 {
  public static void main(String args[]) {
        Test ob = new Test();
        int a = 15, b = 20;
        System.out.println("a and b before call: "
                + a + " " + b);
        ob.meth(a, b);
        System.out.println("a and b after call: "
                + a + " " + b);
    }
}

why these lines

            System.out.println("a=" +i);
            System.out.println("b=" +j);

print a=30 & b=10 As changes made to the parameter of the subroutine have no effect on the argument plz clear my doubts soon.