Problem: program outputs numbers in scientific notation

Question

my problem is that my program outputs the population in scientific notation instead of round the number to the nearest one. ex: it should say 30787949.57 instead of 3.078794957 E7
// Calculates the poulation of Mexico City from 1995 to 2018.
// displays the year and population
class PopulationCalculator {
static double r2(double x) {
     //this method rounds a double value to two decimal places.
double z=((double)(Math.round(x*100)))/100;
return z;
} //end method r2
public static void main(String args[]) {
     double population=15600000.0;
     double rate=0.03;
     System.out.println("Mexico City Population, rate="+r2(rate));
     System.out.println("Year    Population");
     for (int year=1995; year<=2018;year++)  {
         System.out.println(year+ "    "+r2(population));
    population+=rate*population;
    }//end for loop
    System.out.println("The population of Mexico City reaches 30 million on 02/13/17 at 5:38:34am");
    }//end main
    }//end PopulationCalculator
{code/]