如何 return 一个子类独有的变量？

Question

我有 class Person 有多个子class。所有子 class 都有相同的变量（name、address、phone），但有一个有一个额外的变量，rank。我知道如何显示 name、address、phone 但我不知道如何显示 rank.

定义class:

public class Person {
    public String name;
    public String address;
    public String phone;

    public Person(String name, String address, String phone) {
        this.name = name;
        this.address = address;
        this.phone = phone;
    }

    public String toString() {
        return this.getClass().getName() + "\n" + name;
    }
}

用rank定义子class:

public class Pupil extends Person {
    public String rank;
    public Student(String name, String address, String phone, String rank) {
        super(name, social, phone);
    }

}

创建 pupil 并显示 name、address 和 phone。

public class Test {

public static void main(String[] args) {
Person person = new Person("John", "1 John Deer Rd", "1112223333");
Person pupil = new Pupil("Jane", "2 John Deer Rd", "1112223333", "junior");


System.out.println(pupil.name + "'s phone is " + pupil.phone + " and their address is " + pupil.address + "." + "\n");

}
}

如何同时显示 rank？

Answer 1

您可以使用 Pupil 的构造函数代替 Person 的构造函数

public class Pupil extends Person {
    public String rank;
    public Pupil (String name, String address, String phone, String rank) {
        super(name, social, phone);
    }

}
Pupil pupil = new Pupil("Jane", "2 John Deer Rd", "1112223333", "junior");pupil = new Pupil("Jane", "2 John Deer Rd", "1112223333", "junior");
System.out.println(pupil.name + "'s phone is " + pupil.phone + " and their address is " + pupil.address + "." + "\n"+pupil .rank);

我建议使用 getter 和 setter 方法并使用它们并将您的字段设为私有。您可以阅读 more about setter and getter methods 一个简单的例子：

public class Person {
private String name;
public String getName() {
return name;
}
public void setName(String name) {
this.name =name;
//get name parameter and set it to this class'sname parameter }

最后但同样重要的是，我建议您阅读 this keyword 开心点。

Answer 2

您必须将对象从 Person 转换回 Pupil:

((Pupil)pupil).rank

如果您不能 100% 确定您的对象实际上是一个 Pupil，您应该添加完整性检查：

if(pupil instanceof Pupil) {
    System.out.println(…+((Pupil)pupil).rank+…);
}

如何 return 一个子类独有的变量？

How to return variable that is exclusive to one subclass?

java

subclass