code: public class Jensen2 {
  
      interface IntToDoubleFunction {
          double apply(int n);
      }
  
      static double sum(int lo, int hi, IntToDoubleFunction f) {
          double res = 0;
          for (int i = lo; i <= hi; i++)
              res += f.apply(i);
          return res;
  
      }
      public static void main(String args[]) {
          System.out.println(
              sum(1, 100,
                  new IntToDoubleFunction() {
                      public double apply(int i) { return 1.0/i;}
                  }));
      }
  }
  