java用io流定义一个图书类，有id，name，price，author，type，press，，在测试类里实现添加到book.txt文件中，实现查询功能，删除功能，修改功能

首先，我们定义一个Book类，包含id，name，price，author，type，press属性和相关的getter和setter方法。

public class Book {
    private String id;
    private String name;
    private double price;
    private String author;
    private String type;
    private String press;

    public Book() {}

    public Book(String id, String name, double price, String author, String type, String press) {
        this.id = id;
        this.name = name;
        this.price = price;
        this.author = author;
        this.type = type;
        this.press = press;
    }

    // getter and setter methods

    public String getId() {
        return id;
    }

    public void setId(String id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public double getPrice() {
        return price;
    }

    public void setPrice(double price) {
        this.price = price;
    }

    public String getAuthor() {
        return author;
    }

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

    public String getType() {
        return type;
    }

    public void setType(String type) {
        this.type = type;
    }

    public String getPress() {
        return press;
    }

    public void setPress(String press) {
        this.press = press;
    }
}

接下来，我们实现一个BookManager类，负责对book.txt文件进行读取、添加、查询、删除和修改操作。具体代码如下：

import java.io.*;
import java.util.ArrayList;
import java.util.List;

public class BookManager {
    private static final String FILE_NAME = "book.txt";
    private static final String FIELD_SEPARATOR = ",";
    private static final String LINE_SEPARATOR = System.getProperty("line.separator");

    // 读取所有的书籍信息
    public static List<Book> getAllBooks() {
        List<Book> bookList = new ArrayList<>();
        try (BufferedReader reader = new BufferedReader(new FileReader(FILE_NAME))) {
            String line;
            while ((line = reader.readLine()) != null) {
                String[] fields = line.split(FIELD_SEPARATOR);
                if (fields.length == 6) {
                    Book book = new Book(fields[0], fields[1], Double.parseDouble(fields[2]), fields[3], fields[4], fields[5]);
                    bookList.add(book);
                }
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
        return bookList;
    }

    // 添加一本书籍
    public static void addBook(Book book) {
        try (BufferedWriter writer = new BufferedWriter(new FileWriter(FILE_NAME, true))) {
            writer.write(book.getId() + FIELD_SEPARATOR + book.getName() + FIELD_SEPARATOR
                    + book.getPrice() + FIELD_SEPARATOR + book.getAuthor() + FIELD_SEPARATOR
                    + book.getType() + FIELD_SEPARATOR + book.getPress() + LINE_SEPARATOR);
            writer.flush();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    // 根据id查询一本书籍
    public static Book getBookById(String id) {
        try (BufferedReader reader = new BufferedReader(new FileReader(FILE_NAME))) {
            String line;
            while ((line = reader.readLine()) != null) {
                String[] fields = line.split(FIELD_SEPARATOR);
                if (fields.length == 6 && fields[0].equals(id)) {
                    return new Book(fields[0], fields[1], Double.parseDouble(fields[2]), fields[3], fields[4], fields[5]);
                }
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
        return null;
    }

    // 根据id删除一本书籍
    public static void deleteBookById(String id) {
        List<Book> bookList = getAllBooks();
        try (BufferedWriter writer = new BufferedWriter(new FileWriter(FILE_NAME))) {
            for (Book book : bookList) {
                if (!book.getId().equals(id)) {
                    writer.write(book.getId() + FIELD_SEPARATOR + book.getName() + FIELD_SEPARATOR
                            + book.getPrice() + FIELD_SEPARATOR + book.getAuthor() + FIELD_SEPARATOR
                            + book.getType() + FIELD_SEPARATOR + book.getPress() + LINE_SEPARATOR);
                }
            }
            writer.flush();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    // 根据id修改一本书籍的信息
    public static void updateBookById(String id, Book newBook) {
        List<Book> bookList = getAllBooks();
        try (BufferedWriter writer = new BufferedWriter(new FileWriter(FILE_NAME))) {
            for (Book book : bookList) {
                if (book.getId().equals(id)) {
                    writer.write(newBook.getId() + FIELD_SEPARATOR + newBook.getName() + FIELD_SEPARATOR
                            + newBook.getPrice() + FIELD_SEPARATOR + newBook.getAuthor() + FIELD_SEPARATOR
                            + newBook.getType() + FIELD_SEPARATOR + newBook.getPress() + LINE_SEPARATOR);
                } else {
                    writer.write(book.getId() + FIELD_SEPARATOR + book.getName() + FIELD_SEPARATOR
                            + book.getPrice() + FIELD_SEPARATOR + book.getAuthor() + FIELD_SEPARATOR
                            + book.getType() + FIELD_SEPARATOR + book.getPress() + LINE_SEPARATOR);
                }
            }
            writer.flush();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

最后，我们可以在测试类中使用BookManager类的方法进行相关的操作。

public class Test {
    public static void main(String[] args) {
        // 添加一本书籍
        Book book1 = new Book("001", "Java编程思想", 99.0, "Bruce Eckel", "计算机技术", "机械工业出版社");
        BookManager.addBook(book1);

        // 查询一本书籍
        Book book2 = BookManager.getBookById("001");
        System.out.println(book2.getName());

        // 修改一本书籍的信息
        Book newBook = new Book("001", "Java编程思想(第4版)", 109.0, "Bruce Eckel", "计算机技术", "机械工业出版社");
        BookManager.updateBookById("001", newBook);

        // 删除一本书籍
        BookManager.deleteBookById("001");
    }
}