.java图书馆系统，要求模拟实现对数据库的增、删、改、查操作。 利用集合2.要求至少要实现两个业务需求。

好的，我可以给您提供一个简单的Java图书馆系统实现。

首先，我们需要定义一个Book类，它包含书籍的基本属性，如书名、作者、出版日期和ISBN号。然后，我们可以创建一个BookDatabase类，该类将管理所有图书的增、删、改、查操作。

下面是一个简单的实现：

Book.java

public class Book {
    private String title;
    private String author;
    private String publicationDate;
    private String isbn;

    public Book(String title, String author, String publicationDate, String isbn) {
        this.title = title;
        this.author = author;
        this.publicationDate = publicationDate;
        this.isbn = isbn;
    }

    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 getPublicationDate() {
        return publicationDate;
    }

    public void setPublicationDate(String publicationDate) {
        this.publicationDate = publicationDate;
    }

    public String getIsbn() {
        return isbn;
    }

    public void setIsbn(String isbn) {
        this.isbn = isbn;
    }
}

BookDatabase.java

import java.util.ArrayList;
import java.util.List;

public class BookDatabase {
    private List<Book> books;

    public BookDatabase() {
        this.books = new ArrayList<>();
    }

    public void addBook(Book book) {
        books.add(book);
        System.out.println("Book added: " + book.getTitle());
    }

    public void removeBook(String isbn) {
        Book bookToRemove = null;
        for (Book book : books) {
            if (book.getIsbn().equals(isbn)) {
                bookToRemove = book;
                break;
            }
        }
        if (bookToRemove != null) {
            books.remove(bookToRemove);
            System.out.println("Book removed: " + bookToRemove.getTitle());
        } else {
            System.out.println("Book not found");
        }
    }

    public void updateBook(String isbn, Book newBook) {
        Book bookToUpdate = null;
        for (Book book : books) {
            if (book.getIsbn().equals(isbn)) {
                bookToUpdate = book;
                break;
            }
        }
        if (bookToUpdate != null) {
            bookToUpdate.setTitle(newBook.getTitle());
            bookToUpdate.setAuthor(newBook.getAuthor());
            bookToUpdate.setPublicationDate(newBook.getPublicationDate());
            System.out.println("Book updated: " + bookToUpdate.getTitle());
        } else {
            System.out.println("Book not found");
        }
    }

    public void searchBook(String keyword) {
        List<Book> results = new ArrayList<>();
        for (Book book : books) {
            if (book.getTitle().contains(keyword) || book.getAuthor().contains(keyword)) {
                results.add(book);
            }
        }
        if (results.size() > 0) {
            System.out.println("Search results:");
            for (Book book : results) {
                System.out.println(book.getTitle() + " by " + book.getAuthor());
            }
        } else {
            System.out.println("No results found");
        }
    }
}

现在，我们可以创建一个测试类来演示如何使用BookDatabase类：

LibrarySystemTest.java

public class LibrarySystemTest {
    public static void main(String[] args) {
        BookDatabase bookDatabase = new BookDatabase();

        Book book1 = new Book("The Great Gatsby", "F. Scott Fitzgerald", "1925", "978-0743273565");
        Book book2 = new Book("To Kill a Mockingbird", "Harper Lee", "1960", "978-0446310789");
        Book book3 = new Book("1984", "George Orwell", "1949", "978-0451524935");

        bookDatabase.addBook(book1);
        bookDatabase.addBook(book2);
        bookDatabase.addBook(book3);

        bookDatabase.searchBook("Mockingbird");

        Book newBook = new Book("Animal Farm", "George Orwell", "1945", "978-0451526342");
        bookDatabase.updateBook("978-0451524935", newBook);

        bookDatabase.removeBook("978-0743273565");
    }
}

这个测试类将输出以下内容：

Book added: The Great Gatsby
Book added: To Kill a Mockingbird
Book added: 1984
Search results:
To Kill a Mockingbird by Harper Lee
Book updated: 1984
Book removed: The Great Gatsby

在这个简单的示例中，我们演示了如何使用BookDatabase类进行添加、删除、更新和搜索图书的操作。您可以添加更多的功能，以满足您的需求。