解释以下代码:public List<Book> findeByName(String name) {List<Book> result = new ArrayList<Book>() ;for (Book book : books) {} if (book . getName() .equals(name)) fresult. add(book) ;
时间: 2023-06-18 08:07:56 浏览: 53
这段代码是一个方法,输入参数为一个字符串 name,返回类型为 Book 类型的列表 List<Book>。方法的作用是在一个名为 books 的 Book 类型列表中,查找名称等于输入参数 name 的书籍,并将所有符合条件的书籍添加到结果列表 result 中。
具体实现过程如下:
1. 首先创建一个空的结果列表 result,并使用 ArrayList 类型进行实例化。
2. 然后使用 for-each 循环遍历列表 books 中的每一个元素,即每一本书籍。
3. 在循环内部,使用 if 语句判断当前遍历到的书籍的名称是否等于输入参数 name。如果相等,则将该书籍添加到结果列表 result 中。
4. 最后返回结果列表 result。
需要注意的是,该代码存在一处错误,即 if 语句的代码块应该放在 for 循环内部。正确的代码应该是:
```
public List<Book> findeByName(String name) {
List<Book> result = new ArrayList<Book>();
for (Book book : books) {
if (book.getName().equals(name)) {
result.add(book);
}
}
return result;
}
```
相关问题
Java编写图书管理系统的代码
以下是一个简单的 Java 图书管理系统示例:
1. Book 类:
```java
public class Book {
private String id;
private String name;
private String author;
private int price;
public Book(String id, String name, String author, int price) {
this.id = id;
this.name = name;
this.author = author;
this.price = price;
}
public String getId() {
return id;
}
public String getName() {
return name;
}
public String getAuthor() {
return author;
}
public int getPrice() {
return price;
}
}
```
2. BookList 类:
```java
import java.util.ArrayList;
public class BookList {
private ArrayList<Book> books;
public BookList() {
books = new ArrayList<Book>();
}
public void add(Book book) {
books.add(book);
}
public void remove(Book book) {
books.remove(book);
}
public ArrayList<Book> searchByName(String name) {
ArrayList<Book> result = new ArrayList<Book>();
for (Book book : books) {
if (book.getName().equals(name)) {
result.add(book);
}
}
return result;
}
public ArrayList<Book> searchByAuthor(String author) {
ArrayList<Book> result = new ArrayList<Book>();
for (Book book : books) {
if (book.getAuthor().equals(author)) {
result.add(book);
}
}
return result;
}
public ArrayList<Book> getAll() {
return books;
}
}
```
3. Library 类:
```java
import java.util.Scanner;
public class Library {
private BookList bookList;
public Library() {
bookList = new BookList();
}
public void addBook() {
Scanner scanner = new Scanner(System.in);
System.out.print("请输入书籍编号:");
String id = scanner.nextLine();
System.out.print("请输入书籍名称:");
String name = scanner.nextLine();
System.out.print("请输入书籍作者:");
String author = scanner.nextLine();
System.out.print("请输入书籍价格:");
int price = scanner.nextInt();
scanner.nextLine();
Book book = new Book(id, name, author, price);
bookList.add(book);
System.out.println("添加成功!");
}
public void removeBook() {
Scanner scanner = new Scanner(System.in);
System.out.print("请输入要删除的书籍编号:");
String id = scanner.nextLine();
ArrayList<Book> books = bookList.getAll();
for (Book book : books) {
if (book.getId().equals(id)) {
bookList.remove(book);
System.out.println("删除成功!");
return;
}
}
System.out.println("没有找到编号为 " + id + " 的书籍!");
}
public void searchBookByName() {
Scanner scanner = new Scanner(System.in);
System.out.print("请输入要查询的书籍名称:");
String name = scanner.nextLine();
ArrayList<Book> result = bookList.searchByName(name);
if (result.size() == 0) {
System.out.println("没有找到书名为 " + name + " 的书籍!");
} else {
System.out.println("查询结果:");
for (Book book : result) {
System.out.println(book.getId() + " " + book.getName() + " " + book.getAuthor() + " " + book.getPrice());
}
}
}
public void searchBookByAuthor() {
Scanner scanner = new Scanner(System.in);
System.out.print("请输入要查询的书籍作者:");
String author = scanner.nextLine();
ArrayList<Book> result = bookList.searchByAuthor(author);
if (result.size() == 0) {
System.out.println("没有找到作者为 " + author + " 的书籍!");
} else {
System.out.println("查询结果:");
for (Book book : result) {
System.out.println(book.getId() + " " + book.getName() + " " + book.getAuthor() + " " + book.getPrice());
}
}
}
public void printMenu() {
System.out.println("1. 添加书籍");
System.out.println("2. 删除书籍");
System.out.println("3. 按书名查询");
System.out.println("4. 按作者查询");
System.out.println("5. 退出系统");
}
public void run() {
Scanner scanner = new Scanner(System.in);
while (true) {
printMenu();
System.out.print("请选择操作:");
int choice = scanner.nextInt();
scanner.nextLine();
switch (choice) {
case 1:
addBook();
break;
case 2:
removeBook();
break;
case 3:
searchBookByName();
break;
case 4:
searchBookByAuthor();
break;
case 5:
System.out.println("谢谢使用!");
return;
default:
System.out.println("无效操作,请重新选择!");
}
System.out.println();
}
}
}
```
4. Main 类:
```java
public class Main {
public static void main(String[] args) {
Library library = new Library();
library.run();
}
}
```
运行以上代码后,你可以通过控制台输入来添加、删除、查询图书信息。你可以根据需求修改代码实现你自己的图书管理系统。
Java web图书管理系统代码怎么写
这是一个比较大的项目,需要涉及到前端、后端和数据库等多个方面的知识。以下是一个简单的Java web图书管理系统的代码示例,仅供参考:
1. 创建数据库表
首先需要创建相应的数据库表,例如:
```
CREATE TABLE `book` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`name` varchar(255) NOT NULL,
`author` varchar(255) NOT NULL,
`price` double NOT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
```
2. 编写JavaBean类
在Java中创建一个Book类,用于封装书籍的相关信息,例如:
```
public class Book {
private int id;
private String name;
private String author;
private double price;
// 省略get/set方法
}
```
3. 编写DAO类
创建一个BookDAO类,用于实现对数据库的增删改查操作,例如:
```
public class BookDAO {
// JDBC连接
private Connection conn = null;
// SQL语句执行器
private PreparedStatement pstmt = null;
// 结果集
private ResultSet rs = null;
// 构造方法中初始化数据库连接
public BookDAO() {
try {
Class.forName("com.mysql.jdbc.Driver");
conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/book", "root", "123456");
} catch (Exception e) {
e.printStackTrace();
}
}
// 添加书籍
public boolean add(Book book) {
try {
String sql = "INSERT INTO book(name, author, price) VALUES(?, ?, ?)";
pstmt = conn.prepareStatement(sql);
pstmt.setString(1, book.getName());
pstmt.setString(2, book.getAuthor());
pstmt.setDouble(3, book.getPrice());
int result = pstmt.executeUpdate();
if (result > 0) {
return true;
}
} catch (Exception e) {
e.printStackTrace();
}
return false;
}
// 根据ID删除书籍
public boolean delete(int id) {
try {
String sql = "DELETE FROM book WHERE id=?";
pstmt = conn.prepareStatement(sql);
pstmt.setInt(1, id);
int result = pstmt.executeUpdate();
if (result > 0) {
return true;
}
} catch (Exception e) {
e.printStackTrace();
}
return false;
}
// 根据ID修改书籍信息
public boolean update(Book book) {
try {
String sql = "UPDATE book SET name=?, author=?, price=? WHERE id=?";
pstmt = conn.prepareStatement(sql);
pstmt.setString(1, book.getName());
pstmt.setString(2, book.getAuthor());
pstmt.setDouble(3, book.getPrice());
pstmt.setInt(4, book.getId());
int result = pstmt.executeUpdate();
if (result > 0) {
return true;
}
} catch (Exception e) {
e.printStackTrace();
}
return false;
}
// 根据ID查询书籍信息
public Book findById(int id) {
Book book = new Book();
try {
String sql = "SELECT * FROM book WHERE id=?";
pstmt = conn.prepareStatement(sql);
pstmt.setInt(1, id);
rs = pstmt.executeQuery();
if (rs.next()) {
book.setId(rs.getInt("id"));
book.setName(rs.getString("name"));
book.setAuthor(rs.getString("author"));
book.setPrice(rs.getDouble("price"));
}
} catch (Exception e) {
e.printStackTrace();
}
return book;
}
// 查询所有书籍信息
public List<Book> findAll() {
List<Book> list = new ArrayList<>();
try {
String sql = "SELECT * FROM book";
pstmt = conn.prepareStatement(sql);
rs = pstmt.executeQuery();
while (rs.next()) {
Book book = new Book();
book.setId(rs.getInt("id"));
book.setName(rs.getString("name"));
book.setAuthor(rs.getString("author"));
book.setPrice(rs.getDouble("price"));
list.add(book);
}
} catch (Exception e) {
e.printStackTrace();
}
return list;
}
// 关闭数据库连接
public void close() {
try {
if (rs != null) {
rs.close();
}
if (pstmt != null) {
pstmt.close();
}
if (conn != null) {
conn.close();
}
} catch (Exception e) {
e.printStackTrace();
}
}
}
```
4. 编写Servlet类
创建一个BookServlet类,用于接收前端的请求并调用DAO类中的方法进行处理,例如:
```
@WebServlet("/book")
public class BookServlet extends HttpServlet {
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
doGet(request, response);
}
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// 获取请求参数
String action = request.getParameter("action");
int id = Integer.parseInt(request.getParameter("id"));
String name = request.getParameter("name");
String author = request.getParameter("author");
double price = Double.parseDouble(request.getParameter("price"));
// 创建DAO对象
BookDAO dao = new BookDAO();
// 根据请求参数调用相应的方法
if (action.equals("add")) {
// 添加书籍
Book book = new Book();
book.setName(name);
book.setAuthor(author);
book.setPrice(price);
boolean result = dao.add(book);
if (result) {
response.getWriter().print("添加成功");
} else {
response.getWriter().print("添加失败");
}
} else if (action.equals("delete")) {
// 删除书籍
boolean result = dao.delete(id);
if (result) {
response.getWriter().print("删除成功");
} else {
response.getWriter().print("删除失败");
}
} else if (action.equals("update")) {
// 修改书籍信息
Book book = new Book();
book.setId(id);
book.setName(name);
book.setAuthor(author);
book.setPrice(price);
boolean result = dao.update(book);
if (result) {
response.getWriter().print("修改成功");
} else {
response.getWriter().print("修改失败");
}
} else if (action.equals("findById")) {
// 根据ID查询书籍信息
Book book = dao.findById(id);
response.getWriter().print(book);
} else if (action.equals("findAll")) {
// 查询所有书籍信息
List<Book> list = dao.findAll();
response.getWriter().print(list);
}
// 关闭数据库连接
dao.close();
}
}
```
5. 编写前端页面
最后,创建一个前端页面,用于向Servlet发送请求,并显示相应的结果。例如:
```
<!DOCTYPE html>
<html>
<head>
<title>图书管理系统</title>
<meta charset="UTF-8">
</head>
<body>
<form action="book" method="post">
<input type="hidden" name="action" value="add">
<p>书名:<input type="text" name="name"></p>
<p>作者:<input type="text" name="author"></p>
<p>价格:<input type="text" name="price"></p>
<p><input type="submit" value="添加"></p>
</form>
<form action="book" method="post">
<input type="hidden" name="action" value="delete">
<p>ID:<input type="text" name="id"></p>
<p><input type="submit" value="删除"></p>
</form>
<form action="book" method="post">
<input type="hidden" name="action" value="update">
<p>ID:<input type="text" name="id"></p>
<p>书名:<input type="text" name="name"></p>
<p>作者:<input type="text" name="author"></p>
<p>价格:<input type="text" name="price"></p>
<p><input type="submit" value="修改"></p>
</form>
<form action="book" method="post">
<input type="hidden" name="action" value="findById">
<p>ID:<input type="text" name="id"></p>
<p><input type="submit" value="查询"></p>
</form>
<form action="book" method="post">
<input type="hidden" name="action" value="findAll">
<p><input type="submit" value="查询所有"></p>
</form>
</body>
</html>
```
以上是一个简单的Java web图书管理系统的代码示例,仅供参考。实际开发中,需要根据具体需求进行修改和完善。