java面试项目中遇到的难点，03-增删改查实现

在Java中实现增删改查（CRUD）通常涉及到数据库操作。以下是一个简单的例子，使用JDBC来实现对数据库表的CRUD操作。

首先，确保你有一个数据库表，例如：

CREATE TABLE users (
    id INT PRIMARY KEY,
    name VARCHAR(100),
    email VARCHAR(100)
);

然后，使用JDBC实现CRUD操作：

import java.sql.*;
 
public class UserDao {
    private Connection connect = null;
    private PreparedStatement preparedStatement = null;
    private ResultSet resultSet = null;
 
    public UserDao() {
        try {
            // 加载数据库驱动
            Class.forName("com.mysql.cj.jdbc.Driver");
            // 建立数据库连接
            connect = DriverManager.getConnection("jdbc:mysql://localhost:3306/database_name", "username", "password");
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
 
    // 增加用户
    public boolean insert(User user) {
        try {
            String query = "INSERT INTO users (name, email) VALUES (?, ?)";
            preparedStatement = connect.prepareStatement(query);
            preparedStatement.setString(1, user.getName());
            preparedStatement.setString(2, user.getEmail());
            return preparedStatement.executeUpdate() > 0;
        } catch (Exception e) {
            e.printStackTrace();
            return false;
        }
    }
 
    // 删除用户
    public boolean delete(int id) {
        try {
            String query = "DELETE FROM users WHERE id = ?";
            preparedStatement = connect.prepareStatement(query);
            preparedStatement.setInt(1, id);
            return preparedStatement.executeUpdate() > 0;
        } catch (Exception e) {
            e.printStackTrace();
            return false;
        }
    }
 
    // 修改用户
    public boolean update(User user) {
        try {
            String query = "UPDATE users SET name = ?, email = ? WHERE id = ?";
            preparedStatement = connect.prepareStatement(query);
            preparedStatement.setString(1, user.getName());
            preparedStatement.setString(2, user.getEmail());
            preparedStatement.setInt(3, user.getId());
            return preparedStatement.executeUpdate() > 0;
        } catch (Exception e) {
            e.printStackTrace();
            return false;
        }
    }
 
    // 查询用户
    public User search(int id) {
        try {
            String query = "SELECT * FROM users WHERE id = ?";
            preparedStatement = connect.prepareStatement(query);
            preparedStatement.setInt(1