Java图书馆项目中ArrayList无法正确存储Book对象该如何解决？

核心错误点 #

• Book类的title属性误用static修饰：static属性属于类本身，所有Book实例共享同一个title值，每次新建Book对象都会覆盖全局title，导致所有书的标题都变成最后一本的标题
• 字符串相等判断错误：使用==比较字符串只会对比内存地址，不会对比内容，要改用equals()方法
• Library类定义了多余的全局成员private Book book和private String title，借书/还书逻辑中错误使用这个全局book变量，而非遍历过程中匹配到的当前Book实例
• borrowBook遍历逻辑不完善：匹配到对应书籍后没有跳出循环，遍历其他不匹配的书籍时会重复输出错误提示
• printAvailableBooks直接打印ArrayList会输出对象内存地址，需要遍历输出未借出的书籍标题
• 导入语句错误：import package.Book;为无效语法，同包下无需导入Book类

修正后的代码 #

Book类 #

public class Book {
    private boolean borrowed;
    // 去掉static修饰，改为实例属性，每个Book有独立标题
    private String title;

    // 构造方法
    public Book(String title) {
        this.title = title;
        borrowed = false;
    }
    // 标记为已借出
    public void borrowed() {
        borrowed = true;
    }
    // 标记为已归还
    public void returned() {
        borrowed = false;
    }
    public boolean isBorrowed() {
        return borrowed;
    }
    // 去掉static修饰，改为实例方法
    public String getTitle() {
        return title;
    }
}

Library类 #

import java.util.ArrayList;

// 同包下无需导入Book类，删掉错误的import package.Book;
public class Library {
    private String hours;
    private String address;
    // 删掉多余的全局成员 private String title; 和 private Book book;
    private ArrayList<Book> books = new ArrayList<Book>();

    // 构造方法
    public Library(String address) {
        this.address = address;
        hours = "9 am to 5 pm";
    }
    void printOpeningHours() {
        System.out.println(hours);
    }
    void printAddress() {
        System.out.println(address);
    }
    void addBook(Book book) {
        books.add(book);
    }
    void printAvailableBooks() {
        if (books.size() == 0){
            System.out.println("There are no books available");
            return;
        }
        // 遍历输出未借出的书籍
        for (Book book : books) {
            if (!book.isBorrowed()) {
                System.out.println(book.getTitle());
            }
        }
    }
    void borrowBook(String title) {
        boolean bookFound = false;
        for (Book currentBook : books) {
            // 用equals对比字符串内容
            if (currentBook.getTitle().equals(title)) {
                bookFound = true;
                if (!currentBook.isBorrowed()){
                    currentBook.borrowed();
                    System.out.println("Successfully borrowed " + title);
                } else {
                    System.out.println("Sorry, that book is already checked out");
                }
                // 匹配到书就跳出循环
                break;
            }
        }
        if (!bookFound) {
            System.out.println("Sorry, no such book is available");
        }
    }

    void returnBook(String title) {
        for (Book currentBook : books) {
            if (currentBook.getTitle().equals(title)) {
                if (currentBook.isBorrowed()){
                    currentBook.returned();
                    System.out.println("Successfully returned " + title);
                }
                break;
            }
        }
    }


    public static void main(String[] args) {
        // Create two libraries
        Library firstLibrary = new Library("10 Main St.");
        Library secondLibrary = new Library("228 Liberty St.");

        // Add four books to the first library
        firstLibrary.addBook(new Book("The Da Vinci Code"));
        firstLibrary.addBook(new Book("Le Petit Prince"));
        firstLibrary.addBook(new Book("A Tale of Two Cities"));
        firstLibrary.addBook(new Book("The Lord of the Rings"));

        // Print opening hours and the addresses
        System.out.println("Library hours:");
        firstLibrary.printOpeningHours();
        System.out.println("Library addresses:");
        firstLibrary.printAddress();
        System.out.println();
        System.out.println("Library hours:");
        secondLibrary.printOpeningHours();
        System.out.println("Library addresses:");
        secondLibrary.printAddress();
        System.out.println();

        // Try to borrow The Lord of the Rings from both libraries
        System.out.println("Borrowing The Lord of the Rings:");
        firstLibrary.borrowBook("The Lord of the Rings");
        secondLibrary.borrowBook("The Lord of the Rings");
        System.out.println();

        // Print the titles of all available books from both libraries
        System.out.println("Books available in the first library:");
        firstLibrary.printAvailableBooks();
        System.out.println();
        System.out.println("Books available in the second library:");
        secondLibrary.printAvailableBooks();
        System.out.println();

        // Return The Lord of the Rings to the first library
        System.out.println("Returning The Lord of the Rings:");
        firstLibrary.returnBook("The Lord of the Rings");
        System.out.println();
        System.out.println("Books available in the first library after return:");
        firstLibrary.printAvailableBooks();
    }
}

内容的提问来源于stack exchange，提问作者yungstirjoey666