JAVA类的一个实例变量

import java.util.*;
public class SpeciesDemo {

 /**
  * @param args
  */
 //public class Species {
  public  String name;
  public int population;
  public double growthRate;
  
  public void readInput()
  {
   Scanner keyboard = new Scanner(System.in);
   System.out.println("What is the population of the species?");
   population=keyboard.nextInt();
   while (population<0)
   {
    System.out.println("Population cannot be negative.");
    System.out.println("Reenter population:");
    population = keyboard.nextInt();
   }
   System.out.println(
     "Enter growth rate (percent 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 +"%");
  }
// }
 public static void main(String[] args) {
  // TODO Auto-generated method stub
  SpeciesDemo speciesOfTheMonth = new SpeciesDemo();
 
  
  System.out.println("Enter data on the Species of the Month:");
  speciesOfTheMonth.readInput();
  speciesOfTheMonth.writeOutput();
  }

}
之前由于书上分两块来写主函数和类，所以出现了两个CLASS，让我误以为要建立两个类，其实只要一个类就可以了~