java - 如果我创建了父类的数组，如何通过数组对象访问子类的方法？

Question

我正在使用一个程序来帮助我练习编码技能。该程序有以下场景:有一个20名学生的教室，记录了学生的名字、姓氏和年龄。这些学生中有一半参加学校的体育运动。在这里，记录了他们参加过的比赛以及赢得的比赛。 在这个程序中，我有三个类(class):

1. runStudents - 具有 main 方法的类
2. 学生(字符串姓名、字符串姓氏、整数年龄)- 家长类(class)
3. AthleticStudents(字符串名称、字符串姓氏、整数年龄、整数比赛、整数胜利)- 子类别

用户应该能够向对象添加另一场比赛(并获胜)。从提供的代码可以看出，创建了一个数组来存储 20 个 Students 对象。我必须能够访问一个方法来更改数组中的对象，但该方法不在父类(创建对象的类)中。

public class Students
{
    private String name;
    private String surname;
    private int age;

    public Students()
    {   
    }

    public Students(String name, String surname, int age)
    {
        this.name = name;
        this.surname = surname;
        this.age = age;
    }

    public String getName()
    {
        return this.name;
    }

    public String getSurname()
    {
        return this.surname;
    }

    public double getAge()
    {
        return this.age;
    }

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

    public void setSurname(String surname)
    {
        this.surname = surname;
    }

    public void setAge(int age)
    {
        this.age = age;
    }

    public String toString()
    {
        return String.format("name\t\t: %s\nsurname\t\t: %s\nage\t\t: %s", 
        this.name, this.surname, this.age);
    }
}

public class AthleticStudents extends Students
{
    private int races;
    private int victories;

    public AthleticStudents()
    {

    }

    public AthleticStudents(String name, String surname, int age, int 
        races, int victories)
    {
        super(name, surname, age);
        this.races = races;
        this.victories = victories;
    }

    public int getRaces()
    {
        return this.races;
    }

    public int getVictories()
    {
        return this.victories;
    }

    public void setRaces(int races)
    {
        this.races = races;
    }

    public void setVictories(int victories)
    {
        this.victories = victories;
    }    

    public void anotherRace()
    {
        this.races = this.races + 1;
    }   

    public void anotherWin()
    {
        this.victories = this.victories + 1;
    }

    public String toString()
    {
        return super.toString() + String.format("\nnumber of races\t: 
        %s\nnumber of wins\t: %s", this.races, this.victories);
    }
}

public class runStudents
{
    public static void main(String[]args)
    {
        Students[] myStudents = new Students[20];

        myStudents[0] = new Students("John", "Richards", 15);
        myStudents[1] = new AthleticStudents("Eva", "Grey", 14, 3, 1);
        myStudents[2] = new Students("Lena", "Brie", 15);


        for (int i = 0; i < 3; i++)
            System.out.println(myStudents[i].toString() + "\n\n");
    }
}

我希望能够执行以下操作:

AthleticStudents[1].anotherRace();

但不能这样做，因为数组对象是从父类派生的，并且我在子类中声明了该方法。如何将两者联系起来？

Answer 1

我假设您创建了一个父类实例的数组。只需以这种方式转换实例(您最好检查该元素是否是子类的实例):

if (AthleticStudents[1] instanceof AthleticStudents) 
   ((AthleticStudents) AthleticStudents[1]).anotherRace();