Implements keyword in Java

interface Bill
{   public void calculate(int up,int uc);
}
class Moblie implements Bill
{ public void calculate(int up,int uc)
{ System.out.println(up*uc);
}
}

class B
{   public static void main(String arg[])
{   Moblie m =new Moblie();
    m.calculate(5,100);
}

}