What will be the output?

public class Tester {
       public int add(int a, int b)
      {
             return (a+b);
      }
     public static void main(String args[]) {
           int a=10;
           int b=20;
          int sum=0;
          Tester tester= new Tester();
          Tester.add(a,b);
          System.out.println(sum);
       }
}