Java实现：如何将父子类字段值共同存入LibraryItem类型的ArrayList

• 分隔符规则冲突：子类readData里把分隔符设为[,\n]，父类readData又改成\\s?,\\s?，两套规则切换时很容易出现切分错位，触发NoSuchElementException
• 冗余代码无效：Library类的分支里提前给Scanner设置的分隔符，进到子类readData后会被覆盖，完全是无意义的重复操作
• 字段解析错位风险：当前父类、子类的读字段顺序，需要和CSV文件的列顺序严格对齐，一旦列顺序写错，会直接导致类型转换报错、字段值张冠李戴
• 有参构造赋值漏失：Book类的带参构造接收了noOfPages、publisher两个父类字段值，但没有传给父类做赋值，走该构造路径时父类字段全是默认初始值

1. 全局统一分隔符规则 #

把分隔符的设置逻辑前置到Library类创建Scanner的位置，只设置一次就全链路生效，所有readData方法里删掉重复的分隔符代码。
注意：必须用兼容逗号前后带空格的正则\\s*,\\s*，适配大部分CSV导出的格式
修改后的分支代码：

if (typeOfData.equals("Book")) {
    System.out.println(lineOfText);
    Scanner scanner2 = new Scanner(lineOfText);
    // 一次设置，后续读数据全程生效
    scanner2.useDelimiter("\\s*,\\s*");
    LibraryItem libraryItem = new Book();
    libraryItem.readData(scanner2);
    storeItem(libraryItem);
    scanner2.close();
} else if (typeOfData.equals("Periodical")) {
    System.out.println(lineOfText);
    Scanner scanner2 = new Scanner(lineOfText);
    scanner2.useDelimiter("\\s*,\\s*");
    LibraryItem libraryItem = new Periodical();
    libraryItem.readData(scanner2);
    storeItem(libraryItem);
    scanner2.close();
}

2. 对齐解析顺序 #

严格按照「子类独有字段在前、父类公共字段在后」的逻辑写readData方法，保证和CSV列顺序完全匹配：

• 父类LibraryItem的readData方法删掉分隔符设置，按固定顺序读公共字段即可：

public void readData(Scanner scanner2) {
    this.noOfPages = scanner2.nextInt();
    this.publisher = scanner2.next().trim();
    this.title = scanner2.next().trim();
    this.itemCode = scanner2.next().trim();
    this.cost = scanner2.nextInt();
    this.timesBorrowed = scanner2.nextInt();
    this.onLoan = scanner2.nextBoolean();
}

• Book类的readData方法，先读自身独有的author、isbn字段，再调用super读公共字段：

@Override
public void readData(Scanner scanner2) {
    this.author = scanner2.next().trim();
    this.isbn = scanner2.next().trim();
    super.readData(scanner2);
}

• Periodical类的readData方法，先读自身独有的publicationDate字段，再调用super读公共字段：

@Override
public void readData(Scanner scanner2) {
    this.publicationDate = scanner2.next().trim();
    super.readData(scanner2);
}

注意：CSV文件里的列顺序必须和上面的读取顺序严格对应，比如Book行的列必须是「作者,ISBN,页数,出版社,书名,馆藏编号,成本,累计借阅次数,是否在借」，Periodical行的列必须是「出版日期,页数,出版社,书名,馆藏编号,成本,累计借阅次数,是否在借」，不然一定会读错

3. 补全构造的字段传递 #

给LibraryItem增加带所有公共字段的构造方法，修正子类构造漏传父类值的问题：

// LibraryItem 新增的全参构造
public LibraryItem(int noOfPages, String publisher, String title, String itemCode, int cost, int timesBorrowed, boolean onLoan) {
    this.noOfPages = noOfPages;
    this.publisher = publisher;
    this.title = title;
    this.itemCode = itemCode;
    this.cost = cost;
    this.timesBorrowed = timesBorrowed;
    this.onLoan = onLoan;
}

子类构造调用对应的super方法，把所有值正确传递：

// Book 修正后的构造
public Book(String author, String isbn, int noOfPages, String publisher, String title, String itemCode, int cost, int timesBorrowed, boolean onLoan) {
    super(noOfPages, publisher, title, itemCode, cost, timesBorrowed, onLoan);
    this.author = author;
    this.isbn = isbn;
}

// Periodical 修正后的构造
public Periodical(String publicationDate, int noOfPages, String publisher, String title, String itemCode, int cost, int timesBorrowed, boolean onLoan) {
    super(noOfPages, publisher, title, itemCode, cost, timesBorrowed, onLoan);
    this.publicationDate = publicationDate;
}

4. 增加基础容错 #

在Scanner读数据的外层加简单的异常捕获，遇到单条解析失败的行直接打印错误信息跳过，不要因为一行坏数据中断整个文件的读取流程。

内容的提问来源于stack exchange，提问作者The_Liner