如何返回仅属于一个子类的变量？

huangapple
go评论105阅读模式
英文:

How to return variable that is exclusive to one subclass?

问题

  1. 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`。
  3. 定义类：
  4. ```java
  5. public class Person {
  6.     public String name;
  7.     public String address;
  8.     public String phone;
  10.     public Person(String name, String address, String phone) {
  11.         this.name = name;
  12.         this.address = address;
  13.         this.phone = phone;
  14.     }
  16.     public String toString() {
  17.         return this.getClass().getName() + "\n" + name;
  18.     }
  19. }

定义带有rank的子类：

  1. public class Pupil extends Person {
  2.     public String rank;
  4.     public Pupil(String name, String address, String phone, String rank) {
  5.         super(name, address, phone);
  6.         this.rank = rank;
  7.     }
  8. }

创建pupil并显示name，address和phone。

  1. public class Test {
  3.     public static void main(String[] args) {
  4.         Person person = new Person("John", "1 John Deer Rd", "1112223333");
  5.         Pupil pupil = new Pupil("Jane", "2 John Deer Rd", "1112223333", "junior");
  7.         System.out.println(pupil.name + "'s phone is " + pupil.phone + " and their address is " + pupil.address + ".\n");
  8.         System.out.println(pupil.name + "'s rank is " + pupil.rank + ".\n");
  9.     }
  10. }

如何显示rank？

  2. <details>
  3. <summary>英文:</summary>
  5. 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`.
  7. Define class:

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

  1. public Person(String name, String address, String phone) {
  2.     this.name = name;
  3.     this.address = address;
  4.     this.phone = phone;
  5. }
  7. public String toString() {
  8.     return this.getClass().getName() + &quot;\n&quot; + name;
  9. }

}

  2. 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);
}

}

  2. 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");

}
}

  2. How do I also display `rank`?
  4. </details>
  7. # 答案1
  8. **得分**: 1
  10. 你可以使用 Pupil 的构造函数代替 Person 的构造函数
  12. ```java
  13. public class Pupil extends Person {
  14.     public String rank;
  15.     public Pupil(String name, String address, String phone, String rank) {
  16.         super(name, social, phone);
  17.     }
  18. }
  19. Pupil pupil = new Pupil("Jane", "2 John Deer Rd", "1112223333", "junior");
  20. pupil = new Pupil("Jane", "2 John Deer Rd", "1112223333", "junior");
  21. 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：

  1. public class Person {
  2.     private String name;
  3.     public String getName() {
  4.         return name;
  5.     }
  6.     public void setName(String name) {
  7.         this.name = name;
  8.         // 获取名字参数并将其设置为该类的 name 参数
  9. }

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！

英文:

You can use Pupil 's constructor instead of Person's constructor

  1. public class Pupil extends Person {
  2.     public String rank;
  3.     public Pupil (String name, String address, String phone, String rank) {
  4.         super(name, social, phone);
  5.     }
  7. }
  8. Pupil pupil = new Pupil(&quot;Jane&quot;, &quot;2 John Deer Rd&quot;, &quot;1112223333&quot;, &quot;junior&quot;);pupil = new Pupil(&quot;Jane&quot;, &quot;2 John Deer Rd&quot;, &quot;1112223333&quot;, &quot;junior&quot;);
  9. System.out.println(pupil.name + &quot;&#39;s phone is &quot; + pupil.phone + &quot; and their address is &quot; + pupil.address + &quot;.&quot; + &quot;\n&quot;+pupil .rank);

I suggest using getter and setter methods and use them and make your fields private.
You can read more about setter and getter methods
a quick example:

  1. public class Person {
  2. private String name;
  3. public String getName() {
  4. return name;
  5. }
  6. public void setName(String name) {
  7. this.name =name;
  8. //get name parameter and set it to this class&#39;sname parameter }

Last but not least, I recommend that you read about this keyword
be happy.

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：

  1. if (pupil instanceof Pupil) {
  2.     System.out.println(… + ((Pupil)pupil).rank + …);
  3. }
英文:

You have to cast the object from Person back to Pupil:

((Pupil)pupil).rank

And if you are not 100% sure that your object is actually a Pupil you should add a sanity-check:

  1. if(pupil instanceof Pupil) {
  2.     System.out.println(…+((Pupil)pupil).rank+…);
  3. }

huangapple
  • 本文由 发表于 2020年4月8日 22:19:59
  • 转载请务必保留本文链接：https://go.coder-hub.com/61102962.html
  • java
  • subclass
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