java - 将子类中的对象放入父类(super class)类型的数组后如何调用子类方法？

Question

我有 2 个类 - “Student”和“Employee”，它们都扩展了 Person 类。 所有 3 个类都有内部方法。 在我的演示类中，我必须从每个类(学生、员工和人员)创建 2 个对象，并将它们放入 Person 类型的数组中。然后我必须遍历数组，并根据对象是否来自学生、员工或人员，我必须调用此类/子类中的方法。问题是，一旦这些对象进入 Person 数组，只有 Person 类中的 .methods 可见。如果我的 array[i]."method"来自学生或员工(array[i].showStudentInfo() 和 array[i].showEmplyeeInfo())，如何才能找到它 预先感谢您!

public class Person {
    String name;
    int age;
    boolean isMan;

    Person(String name, int age, boolean isMan) {
        this.name = name;
        this.age = age;
        this.isMan = isMan;
    }

    void showPersonInfo() {
        System.out.println("Име: " + this.name + " | " + "години: " + this.age + " | " + "мъж ли е: " + this.isMan);
    }
}

public class Student extends Person {
    double score;

    Student(String name, int age, boolean isMan, double score) {
        super(name, age, isMan);
        this.score = score;
    }
    public void showStudentInfo() {
        System.out.println("Име: " + super.name + " | " + "години: " + super.age + " | " + "мъж ли е: " + " | "
                + super.isMan + " | " + "Оценка: " + this.score);
    }
}

public class Employee extends Person {
double daySallary;
double extraSum;
Employee(String name, int age, boolean isMan, double daySallary){
    super(name, age, isMan);
    this.daySallary=daySallary;
}
    double calculateOvertime(double hours) {
        if (this.age< 18)
            extraSum = 0;
        else
            extraSum = (this.daySallary / 8) * hours * 1.5;
        return extraSum;
    }
    public void showEmployeeInfo() {
        System.out.println("Име: " + super.name + " | " + "години: " + super.age + " | " + "мъж ли е: " + " | "
                + super.isMan + " | " + "Допълнителна сума от оставане след работно време: " + this.extraSum);
    }
}

public class Demo {
    public static void main(String[] args) {
        Person ivan = new Person("Ivan Georgiev", 27, true);
        Person nikola = new Person("Nikola Ivanov", 30, true);
        Student iskra = new Student("Iskra Dimitrova", 21, false, 4.5);
        Student georgi = new Student("Georgi Kazakov", 19, true, 5.5);
        Employee neli = new Employee("Anelia Stoicheva", 35, false, 50);
        Employee monika = new Employee("Monika Petrova", 42, false, 80);

        Person[] array = new Person[10];
        array[0] = ivan;
        array[1] = nikola;
        array[2] = iskra;
        array[3] = georgi;
        array[4] = neli;
        array[5] = monika;


        for (int i = 0; i < 6; i++) {
            if (array[i].getClass().equals(ivan.getClass())) {
                array[i].showPersonInfo();
            }
            if (array[i].getClass().equals(iskra.getClass())) {

                array[i].showStudentInfo();
            }
            if (array[i].getClass().equals(neli.getClass())) {

                array[i].showEmployeeInfo();
            }
        }

Answer 1

就您而言，由于您已经确认在循环的每次迭代期间正在处理的 Person 类型，因此您可以根据需要将 Person 简单地转换为 Employee 或 Student:

if (array[i].getClass().equals(iskra.getClass())) {
    ((Student)array[i]).showStudentInfo();
}

<小时/>

但是，更好的想法是遵循更标准的面向对象编程模型。由于从 Person 扩展的所有类都有一个显示信息的方法，因此您应该在 Person 类中声明该方法并让子级重写它。

通过在 Person 类中声明 showInfo() 方法，您可以确保您的 for 循环可以访问该方法，无论您使用的是哪种类型的 Person。

<小时/>

人员类别:

public class Person {

    String name;
    int age;
    boolean isMan;

    Person(String name, int age, boolean isMan) {
        this.name = name;
        this.age = age;
        this.isMan = isMan;
    }

    public void showInfo() {
        System.out.println("Име: " + this.name + " | " + "години: " + this.age + " | " + "мъж ли е: " + this.isMan);
    }

    // SETTERS and GETTERS
}

学生类(class):

public class Student extends Person {

    double score;

    Student(String name, int age, boolean isMan, double score) {
        super(name, age, isMan);
        this.score = score;
    }

    @Override
    public void showInfo() {
        System.out.println("Име: " + super.name + " | " + "години: " + super.age + " | " + "мъж ли е: " + " | "
                + super.isMan + " | " + "Оценка: " + this.score);
    }

    // SETTERS and GETTERS
}

员工类别:

public class Employee extends Person {

    double daySallary;
    double extraSum;

    Employee(String name, int age, boolean isMan, double daySallary) {
        super(name, age, isMan);
        this.daySallary = daySallary;
    }

    double calculateOvertime(double hours) {
        if (this.age < 18)
            extraSum = 0;
        else
            extraSum = (this.daySallary / 8) * hours * 1.5;
        return extraSum;
    }

    @Override
    public void showInfo() {
        System.out.println("Име: " + super.name + " | " + "години: " + super.age + " | " + "мъж ли е: " + " | "
                + super.isMan + " | " + "Допълнителна сума от оставане след работно време: " + this.extraSum);
    }
}

<小时/>

从那里，您可以更新您的 Demo 类，以简单地调用每个 Person 上的 showInfo() 方法，而不必首先专门检查 Person 的类型:

for (i = 0; i < array.length; i++) {
  array[i].showInfo();
}