问题

我有一个名为`Person`的类，它有多个子类。所有的子类都有相同的变量（`name`，`address`，`phone`），但其中一个子类有一个额外的变量，`rank`。我知道如何显示`name`，`address`，`phone`，但我不知道如何显示`rank`。

定义类：
```java
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;
    }
}

定义带有rank的子类：

public class Pupil extends Person {
    public String rank;

    public Pupil(String name, String address, String phone, String rank) {
        super(name, address, phone);
        this.rank = rank;
    }
}

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");
        Pupil 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");
        System.out.println(pupil.name + "'s rank is " + pupil.rank + ".\n");
    }
}

如何显示rank？

<details>
<summary>英文:</summary>

I have class `Person` which has multiple subclasses. All subclasses have the same variables (`name`, `address`, `phone`), but one has an extra variable, `rank`. I know how to display `name`, `address`, `phone` but I don&#39;t know how to display `rank`.

Define 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;
}

}

Define the subclass with `rank`:

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

}

Create `pupil` and display `name`, `address`, and `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");

}
}

How do I also display `rank`?

</details>


# 答案1
**得分**: 1

你可以使用 Pupil 的构造函数代替 Person 的构造函数

```java
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，将字段设为私有。您可以阅读有关 getter 和 setter 方法的更多信息。以下是一个快速示例：

public class Person {
    private String name;
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
        // 获取名字参数并将其设置为该类的 name 参数
}

最后但同样重要的是，我建议您阅读有关 this 关键字 的内容。祝您开心！

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);

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 }

答案2

得分: 1

你必须将对象从Person转换回Pupil：

((Pupil)pupil).rank

如果你不是100%确定你的对象实际上是一个Pupil，你应该添加一个健全性检查：

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

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