java实现借书和再借书，借书结束后返回一共借了多少本书

假设你有一个书籍类 Book，其中包含书名、作者、出版社、ISBN、借阅状态等信息。你可以创建一个 BookManager 类来管理图书的借阅和归还，示例代码如下：

public class Book {
    private String title;
    private String author;
    private String publisher;
    private String ISBN;
    private boolean isBorrowed;

    public Book(String title, String author, String publisher, String ISBN) {
        this.title = title;
        this.author = author;
        this.publisher = publisher;
        this.ISBN = ISBN;
        this.isBorrowed = false;
    }

    public String getTitle() {
        return title;
    }

    public void setTitle(String title) {
        this.title = title;
    }

    public String getAuthor() {
        return author;
    }

    public void setAuthor(String author) {
        this.author = author;
    }

    public String getPublisher() {
        return publisher;
    }

    public void setPublisher(String publisher) {
        this.publisher = publisher;
    }

    public String getISBN() {
        return ISBN;
    }

    public void setISBN(String ISBN) {
        this.ISBN = ISBN;
    }

    public boolean isBorrowed() {
        return isBorrowed;
    }

    public void setBorrowed(boolean borrowed) {
        isBorrowed = borrowed;
    }
}


public class BookManager {
    private List<Book> books;
    private int borrowedCount;

    public BookManager(List<Book> books) {
        this.books = books;
        this.borrowedCount = 0;
    }

    public void borrowBook(Book book) {
        if (!book.isBorrowed()) {
            book.setBorrowed(true);
            borrowedCount++;
            System.out.println("借阅成功：" + book.getTitle());
        } else {
            System.out.println("该书已被借出：" + book.getTitle());
        }
    }

    public void returnBook(Book book) {
        if (book.isBorrowed()) {
            book.setBorrowed(false);
            borrowedCount--;
            System.out.println("归还成功：" + book.getTitle());
        } else {
            System.out.println("该书未被借出：" + book.getTitle());
        }
    }

    public int getBorrowedCount() {
        return borrowedCount;
    }
}

在这个例子中，Book 类表示一本书的基本信息，包括书名、作者、出版社、ISBN 和借阅状态。BookManager 类管理图书的借阅和归还，同时维护一个 borrowedCount 变量来记录当前已借出的书籍数量。

你可以创建一个 BookManager 实例，并通过 borrowBook 和 returnBook 方法来借阅和归还图书。调用 getBorrowedCount 方法，可以返回当前已借出的书籍数量。

示例代码如下：

public static void main(String[] args) {
    Book book1 = new Book("Java编程思想", "Bruce Eckel", "机械工业出版社", "9787111407010");
    Book book2 = new Book("Effective Java", "Joshua Bloch", "机械工业出版社", "9787111407898");
    Book book3 = new Book("Java核心技术", "Cay S. Horstmann", "机械工业出版社", "9787111591109");

    List<Book> books = new ArrayList<>();
    books.add(book1);
    books.add(book2);
    books.add(book3);

    BookManager manager = new BookManager(books);

    manager.borrowBook(book1);
    manager.borrowBook(book1); // 重复借阅同一本书
    manager.borrowBook(book2);
    manager.returnBook(book3); // 归还未被借出的书籍
    manager.returnBook(book1);
    manager.returnBook(book2);

    System.out.println("已借出书籍数量：" + manager.getBorrowedCount());
}

输出结果如下：

借阅成功：Java编程思想
该书已被借出：Java编程思想
借阅成功：Effective Java
该书未被借出：Java核心技术
归还成功：Java编程思想
归还成功：Effective Java
已借出书籍数量：0

在这个例子中，我们创建了三本书，然后创建了一个 BookManager 实例来管理这些书。通过 borrowBook 方法借阅书籍，通过 returnBook 方法归还书籍。最后调用 getBorrowedCount 方法，返回借出的书籍数量。