用java实现数据库的增删改查

数据库的增删改查可以通过 JDBC 技术实现，以下是 Java 代码示例：

先定义一个数据库连接的工具类 `DBUtil`：

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;

public class DBUtil {
    private static final String URL = "jdbc:mysql://localhost:3306/test";
    private static final String USER = "root";
    private static final String PASSWORD = "root";

    public static Connection getConnection() {
        Connection conn = null;
        try {
            Class.forName("com.mysql.jdbc.Driver");
            conn = DriverManager.getConnection(URL, USER, PASSWORD);
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        } catch (SQLException e) {
            e.printStackTrace();
        }
        return conn;
    }
}

然后，我们可以通过以下 Java 代码实现数据库的增删改查：

import java.sql.*;

public class CRUD {
    public static void main(String[] args) {
        Connection conn = null;
        PreparedStatement pstmt = null;
        ResultSet rs = null;
        try {
            // 获取数据库连接
            conn = DBUtil.getConnection();

            // 插入数据
            String sqlInsert = "INSERT INTO user(name, age) VALUES (?, ?)";
            pstmt = conn.prepareStatement(sqlInsert);
            pstmt.setString(1, "Tom");
            pstmt.setInt(2, 20);
            int resultInsert = pstmt.executeUpdate();
            System.out.println("插入数据的行数：" + resultInsert);

            // 查询数据
            String sqlSelect = "SELECT * FROM user WHERE age > ?";
            pstmt = conn.prepareStatement(sqlSelect);
            pstmt.setInt(1, 18);
            rs = pstmt.executeQuery();
            while (rs.next()) {
                System.out.println("姓名：" + rs.getString("name") + "，年龄：" + rs.getInt("age"));
            }

            // 更新数据
            String sqlUpdate = "UPDATE user SET age = ? WHERE name = ?";
            pstmt = conn.prepareStatement(sqlUpdate);
            pstmt.setInt(1, 21);
            pstmt.setString(2, "Tom");
            int resultUpdate = pstmt.executeUpdate();
            System.out.println("更新数据的行数：" + resultUpdate);

            // 删除数据
            String sqlDelete = "DELETE FROM user WHERE age = ?";
            pstmt = conn.prepareStatement(sqlDelete);
            pstmt.setInt(1, 20);
            int resultDelete = pstmt.executeUpdate();
            System.out.println("删除数据的行数：" + resultDelete);

        } catch (SQLException e) {
            e.printStackTrace();
        } finally {
            try {
                if (rs != null) {
                    rs.close();
                }
                if (pstmt != null) {
                    pstmt.close();
                }
                if (conn != null) {
                    conn.close();
                }
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
    }
}

运行程序后，可以看到插入数据、查询数据、更新数据和删除数据的结果。需要注意的是，这里的 SQL 语句以及表名、列名等信息都需要根据实际情况修改。