jdbc增删改查代码怎么写

下面是一个简单的示例代码，演示如何使用JDBC进行增删改查操作：

1、增加数据：

Connection conn = DriverManager.getConnection(url, username, password);
String sql = "INSERT INTO table_name (column1, column2) VALUES (?, ?)";
PreparedStatement stmt = conn.prepareStatement(sql);
stmt.setString(1, "value1");
stmt.setString(2, "value2");
stmt.executeUpdate();
conn.close();

2、删除数据：

Connection conn = DriverManager.getConnection(url, username, password);
String sql = "DELETE FROM table_name WHERE column1 = ?";
PreparedStatement stmt = conn.prepareStatement(sql);
stmt.setString(1, "value1");
stmt.executeUpdate();
conn.close();

3、更新数据：

Connection conn = DriverManager.getConnection(url, username, password);
String sql = "UPDATE table_name SET column1 = ? WHERE column2 = ?";
PreparedStatement stmt = conn.prepareStatement(sql);
stmt.setString(1, "new_value");
stmt.setString(2, "value2");
stmt.executeUpdate();
conn.close();

4、查询数据：

Connection conn = DriverManager.getConnection(url, username, password);
String sql = "SELECT * FROM table_name WHERE column1 = ?";
PreparedStatement stmt = conn.prepareStatement(sql);
stmt.setString(1, "value1");
ResultSet rs = stmt.executeQuery();

while (rs.next()) {
    System.out.println(rs.getString("column1"));
    System.out.println(rs.getString("column2"));
}

conn.close();

请注意，以上示例代码是基于JDBC API，需要导入相应的包，并且需要替换相应的url、username、password、table_name、column和value等信息。