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我需要从以下类列表 (Species.java) 中访问私有变量，以便在 KlingonOx.java 类中使用它们。

KlingonOx.java 类的目的是确定在多少年后大象物种的数量将大于克林贡牛物种的数量。

这是 Species.java 类：

import java.util.Scanner;

public class Species
{
private String name;
private int population;
private 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();

    while(population < 0)
    {
        System.out.println("Population cannot be negative.");
        System.out.println("Reenter population:");
        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 + "%");
}

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;
}

public Species(String name)
{
    name = name;
    population = 0;
    growthRate = 0.0;
}

public Species(int population)
{
    name = "";
    if (population > 0)
        population = population;
    else
    {
        System.out.println("ERROR: using a negative" + "population.");
        System.exit(0);
    }
    growthRate = 0.0;
}

public Species(double growthRate)
{
    name = "";
    population = 0;
    growthRate = growthRate;
}

public Species(String name, int population, double growthRate)
{
    name = name;
    if (population > 0)
        population = population;
    else
    {
        System.out.println("ERROR: using a negative" + "population.");
        System.exit(0);
    }
    growthRate = growthRate;
}

public Species()
{
    name = "";
    population = 0;
    growthRate = 0;
}

public void setSpecies(String newName, int newPopulation, double newGrowthRate)
{
    name = newName;
    if (newPopulation >= 0)
        population = newPopulation;
    else
    {
        System.out.println("ERROR: using a negative " + "population.");
        System.exit(0);
    }

    growthRate = newGrowthRate;
}

public void setName(String name)
{
    name = name;
}

public void setPopulation(int population)
{
    if (population > 0)
        population = population;
    else
    {
        System.out.println("ERROR: using a negative" + "population."); 
        System.exit(0);
    }
}

public void setGrowthRate(double growthRate)
{
    growthRate = growthRate;
}

public String getName()
{
    return name;
}

public int getPopulation()
{
    return population;
}

public double getGrowthRate()
{
    return growthRate;
}

public boolean equals(Species otherObject)
{
    return (name.equalsIgnoreCase(otherObject.name)) &&
           (population == otherObject.population) &&
           (growthRate == otherObject.growthRate);
}
}

这是 KlingonOx.java 类：

import java.util.Scanner;
public class KlingonOx extends Species
{
public static void main(String[] args) 
{
    new KlingonOx().run();
}

public void run()
{     
    Species klingonox = new Species();
    Species elephant = new Species();

    System.out.println("Please enter data on the species Klingon Ox."); 
    klingonox.readInput();
    klingonox.writeOutput();
    klingonox.setPopulation(int population);
    population = population;
    klingonox.setGrowthRate(double growthRate);
    growthRate = growthRate;

    System.out.println("Please enter data on the species Elephant.");
    elephant.readInput(); 
    elephant.writeOutput();
    elephant.setPopulation(population);
    population = population;
    elephant.setGrowthRate(growthRate);
    growthRate = growthRate;

    int year = 0;
    if(klingonox.population < elephant.population)
    {
        while(klingonox.population < elephant.population)
        {
            klingonox.population = (int)(klingonox.population + (klingonox.population * (klingonox.growthRate/100) ) );
            elephant.population=(int)(elephant.population + (elephant.population * (elephant.growthRate/100) ) );
            year++;
        }

        System.out.println("KLINGON OX EXCEEDS ELEPHANT IN" + year + "YEARS");
    }

    else
    {
        while(klingonox.population > elephant.population)
        {
            klingonox.population=(int)(klingonox.population+(klingonox.population*(klingonox.growthRate/100)));
            elephant.population=(int)(elephant.population+(elephant.population*(elephant.growthRate/100)));
            year++;
        }
    System.out.println("ELEPHANT EXCEEDS KLINGON OX IN" + year + "YEARS");
    }
}
}

KlingonOx.java 类给我的错误是“population”和“growthRate”是 Species 中的私有实例变量，因此无法访问。我尝试使用 getPopulation 和 getGrowthRate 方法调用来检索变量，但我不确定如何正确执行此操作。

任何反馈表示赞赏。

4

6 回答 6

7

在有变量的类中：

class Foo {
  private int variable;

  public int getVariable() { return variable; }
}

在客户端类中：

class Bar {
   void method() {
     ...
     Foo foo = new Foo();
     int population = foo.getVariable();
     ...
   }
}

这几乎就是一切。

于 2012-12-10T02:51:09.267 回答
2

而不是 using klingonox.population，您应该使用klingonox.getPopulation()- 您的其他Species对象也是如此。

getPopulation这应该是您使用该方法所需进行的唯一更改。

于 2012-12-10T02:49:14.103 回答
1

第一的，

klingonox.setPopulation(int population);
population = population;
klingonox.setGrowthRate(double growthRate);
growthRate = growthRate;

如果您正在设置人口，请传递值 klingonox.setPopulation(20) 以及为什么要尝试将人口分配给人口。克林贡牛没有野外种群。当您调用 readInput(); 时，您的人口名称和growthRate 应该已经分配；

大象对象也是如此。

于 2012-12-10T03:26:01.933 回答
0

采用

klingonox.getPopulation();
于 2012-12-10T02:50:07.207 回答
0

private访问修饰符允许我们隐藏一个变量，以便声明它的类只能被访问。你上课——

public class Species {
 private String name;
 private int population;
 private double growthRate;

 public int getPopulation(){return population;}
 public double growthRate(){return growthRate;}
}

这个概念也称为封装，我们使用public方法来访问和修改private变量。

于 2012-12-10T02:57:35.317 回答
0

-您想instance variable从-Class 访问Super-Class Sub。

-使用super关键字，Getter-Setter方法。

例如：

public class Species
{
private String name;
private int population;
private double growthRate;

public int getPopulation(){

return this.population;

}

public double getGrowthRate(){

return this.growthRate;

}

public String getName(){

return this.name;

}

// Setters...........

}


public class KlingonOx extens Spices{

.......
.......

  public static void main(String[] args){


       int p = super.getPopulation();

       ........
       ........
    }


}
于 2012-12-10T03:10:11.697 回答