Understanding the Question

Question

I'm working on an assignment and I don't quite understand the instructors question on what she's looking for. I'll post it in several posts due to the forums post restrictions.
Question:
Modify SpeciesSecondTry by adding the fourth feature, averageLifespan (as double), to a species and revise SpeciesSecondTryDemo accordingly.
Problem:
I would imagine to get an average life span you would add the total years of all the species and divide by the number of species. I do not see how I can make a mathmatical equation from this code.
Additionally, SpeciesSecondTryDemo is returning an error regarding printing. Have I not defined .average the same way as .name, etc?
E:\WU\CSC117 Java II\Exercise 2\SpeciesSecondTryDemo.java:31: cannot find symbol
symbol  : variable average
location: class SpeciesSecondTry
         System.out.println("The average life span of the " +speciesOfTheMonth.name +" is " +speciesOfTheMonth.average);
                                                                                                              ^
1 errorSpeciesSecondTryDemo.java
public class SpeciesSecondTryDemo
    public static void main(String[] args)
        SpeciesSecondTry speciesOfTheMonth = new SpeciesSecondTry( );
        System.out.println("Enter data on the Species of the Month:");
        speciesOfTheMonth.readInput( );
        speciesOfTheMonth.writeOutput( );
        int futurePopulation = speciesOfTheMonth.predictPopulation(10);
        System.out.println("In ten years the population will be " +
                            futurePopulation);
        //Change the species to show how to change
        //the values of instance variables:
          speciesOfTheMonth.name = "Klingon Ox";
        speciesOfTheMonth.population = 10;
        speciesOfTheMonth.growthRate = 15;
        System.out.println("The new Species of the Month:");
        speciesOfTheMonth.writeOutput( );
        System.out.println("In ten years the population will be " +
                            speciesOfTheMonth.predictPopulation(10));
//I've add this below
         speciesOfTheMonth.averageLifeSpan( );
         System.out.println("The average life span of the " +speciesOfTheMonth.name +" is " +speciesOfTheMonth.average);
}

Answer 1

SpeciesSecondTry.java
import java.util.Scanner;
public class SpeciesSecondTry
    public String name;
    public int population;
    public double growthRate;
    public void readInput( )
        Scanner keyboard = new Scanner(System.in);
        System.out.println("What is the species' name?");
        name = keyboard.nextLine( );
        System.out.println("What is the population of the species?");
        population = keyboard.nextInt( );
        System.out.println("Enter growth rate (% increase per year):");
        growthRate = keyboard.nextDouble( );
    public void writeOutput( )
         System.out.println("Name = " + name);
         System.out.println("Population = " + population);
         System.out.println("Growth rate = " + growthRate + "%");
     Returns the projected population of the calling object
     after the specified number of years.
    public int predictPopulation(int years)
          int result = 0;
        double populationAmount = population;
        int count = years;
        while ((count > 0) && (populationAmount > 0))
            populationAmount = (populationAmount +
                          (growthRate / 100) * populationAmount);
            count--;
        if (populationAmount > 0)
            result = (int)populationAmount;
        return result;
//I've added averageLifeSpan as a double below.
    public double averageLifeSpan()
               Scanner keyboard = new Scanner(System.in);
               System.out.println("What is the average life span of the " +name + " species?");
               double average = keyboard.nextDouble( );
               return average;
}