Unit 5 Writing Classes | 现代数学启蒙

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Java Class Example: Student

The code provided defines a Java class named Student that models the properties and behaviors of a student object. Let's break it down part by part:

Class Definition and Purpose:

This introduces the Student class with a comment explaining its purpose, which is to model a student in terms of properties (like name and ID) and behaviors (such as adding grades and calculating averages).

Instance Variables (Fields):

name and studentID are strings representing the student's name and ID.

grades is an array of doubles to store the student's grades.

numGrades is an integer to track how many grades have actually been entered into the grades array.

Constructor:

The constructor initializes a new instance of Student with the provided name and studentID, sets up an array to hold up to 10 grades, and initializes numGrades to 0.

Accessor Methods (Getters):

These methods allow external code to get the values of the name and studentID fields.

Mutator Methods (Setters):

These methods allow external code to set new values for the name and studentID.

Adding Grades:

Adds a new grade to the grades array if there is space. If the array is full, it outputs a message indicating no space is available.

Calculating Average:

Computes the average of the grades stored. It first checks if there are any grades to avoid division by zero.

Displaying Information:

Outputs the student's name, ID, and average grade to the console.

Main Method:

This method is used to run the class, demonstrating its functionality by creating a Student instance, adding some grades, and then displaying the student's details and average grade.

Overall, the code provides a comprehensive example of a simple Java class with encapsulation, constructors, methods, and a main method for demonstration.

Here's another detailed example that shows the anatomy of a class in Java, covering constructors, instance variables, methods, and encapsulation principles:

Java Class Example: Book

The Java code above defines a class named Book that models the properties and behaviors of a book object. Here's a breakdown of each part of the code:

Class Declaration

public class Book: Declares a public class named Book.

Instance Variables (Fields)

Instance Variables: These are properties of a Book object. They are declared as private to ensure encapsulation, which means the data can only be accessed through methods of the class.

title: Stores the title of the book.
author: Stores the name of the author.
pageCount: Stores the number of pages in the book.
isAvailable: A boolean indicating the availability of the book.

Constructor

Constructor: This method initializes a new instance of the Book class with specific values for title, author, and page count. It sets isAvailable to true by default.

this keyword is used to refer to the current object instance.

Accessor Methods (Getters)

Getters: These methods provide read access to the instance variables. They return the value of each field.

Mutator Methods (Setters)

Setters: These methods allow the modification of the instance variables. They perform updates to the fields, like changing the title or the number of pages. The setPageCount method includes a check to ensure that the page count is positive.

Display Method

displayInfo: This method prints the details of the book to the console.

Main Method

main method: This is the entry point of the program where an instance of Book is created with the title "1984" by George Orwell, containing 328 pages. It displays the book details, updates the availability, and then displays the updated information.

翻译：

下面是一个名为 Student 的 Java 类，它模拟了具有姓名、ID 和成绩等属性的学生。本例包括构造函数、实例变量、用于获取和设置这些变量的方法，以及一个计算平均成绩的方法。

Java 类示例：Student

Java

提供的代码定义了一个名为 Student 的 Java 类，它模拟了学生对象的属性和行为。让我们逐部分分解它：

类定义和目的：

Java

这段代码引入了 Student 类，并通过注释解释了其目的，即从属性（如姓名和 ID）和行为（如添加成绩和计算平均成绩）来模拟一个学生。

实例变量（字段）：

Java

name 和 studentID 是表示学生姓名和 ID 的字符串。

grades 是一个 double 类型的数组，用于存储学生的成绩。

numGrades 是一个整数，用于跟踪已经输入到 grades 数组中的成绩数量。

构造函数：

Java

构造函数使用提供的 name 和 studentID 初始化一个新的 Student 实例，设置一个数组以容纳最多 10 个成绩，并将 numGrades 初始化为 0。

访问器方法（getters）：

Java

这些方法允许外部代码获取 name 和 studentID 字段的值。

修改器方法（setters）：

Java

这些方法允许外部代码为 name 和 studentID 设置新值。

添加成绩：

Java

如果有空间，则将新成绩添加到 grades 数组中。如果数组已满，它会输出一条消息，指示没有可用空间。

计算平均值：

Java

计算存储的成绩的平均值。它首先检查是否有任何成绩，以避免被零除。

显示信息：

Java

将学生的姓名、ID 和平均成绩输出到控制台。

主方法：

Java

此方法用于运行该类，通过创建一个 Student 实例，添加一些成绩，然后显示学生的详细信息和平均成绩，来演示其功能。

总的来说，该代码提供了一个简单 Java 类的全面示例，包括封装、构造函数、方法和用于演示的主方法。

下面是另一个详细的示例，展示了 Java 中一个类的结构，涵盖了构造函数、实例变量、方法和封装原则：

Java 类示例：Book

Java

上述 Java 代码定义了一个名为 Book 的类，它模拟了图书对象的属性和行为。下面是对代码各部分的分解：

类声明

Java

public class Book：声明了一个名为 Book 的公共类。

实例变量（字段）

Java

实例变量：这些是 Book 对象的属性。它们被声明为私有，以确保封装性，这意味着数据只能通过类的方法访问。

title：存储图书的标题。

author：存储作者的姓名。

pageCount：存储图书的页数。

isAvailable：一个布尔值，指示图书的可用性。

构造函数

Java

构造函数：该方法使用特定的标题、作者和页数值初始化 Book 类的新实例。它将 isAvailable 默认设置为 true。

this 关键字用于引用当前对象实例。

访问器方法（getters）

Java

Getters：这些方法提供对实例变量的读取访问。它们返回每个字段的值。

修改器方法（setters）

Java

Setters：这些方法允许修改实例变量。它们对字段进行更新，比如更改标题或页数。setPageCount 方法包括一个检查，以确保页数为正数。

显示方法

Java

displayInfo：该方法将图书的详细信息打印到控制台。

主方法

Java

main 方法：这是程序的入口点，在这里创建了一个名为 "1984"、作者为 George Orwell、页数为 328 的 Book 实例。它显示图书详细信息，更新可用性，然后显示更新后的信息。

Student类（纯代码）：

Book类（纯代码）：