Mysql數據庫異常

Question

異常在線程 「主要」 java.lang.Error的：未解決的問題，編譯： 類型不匹配：不能從java.sql.Statement中轉換爲com.mysql.jdbc.Statement

i am a beginner in java i am trying to use mysql database i have downloaded mysql-connector-java-5.1.23-bin.jar file from mysql.com and i have added this jar file to in my build path of my project but there is an error in the following code Exception in thread "main" java.lang.Error: Unresolved compilation problem: Type mismatch: cannot convert from java.sql.Statement to com.mysql.jdbc.Statement

---

package com.example.demo; 

import java.sql.DriverManager; 
import java.sql.ResultSet; 
import java.sql.SQLException; 

import com.mysql.jdbc.Connection; 
import com.mysql.jdbc.Statement; 

public class DBConnect 
{ 
private static final String userName = "root"; 
private static final String userpwd = "sverma"; 
private static final String CONN_STR = "jdbc:mysql://localhost:3306/phpweb_db"; 

public static void main(String[] args) throws SQLException 
{ 

    Connection conn = null; 
    Statement st = null; 
    ResultSet rs = null; 

    try 
    { 
     DriverManager.getConnection(CONN_STR, userName, userpwd); 
     st=conn.createStatement(ResultSet.TYPE_SCROLL_INSENSITIVE,ResultSet.CONCUR_READ_ONLY); 
     rs = st.executeQuery("select * from user"); 
     rs.last(); 
     System.out.println("No of rows: " + rs.getRow()); 

     // System.out.println("Connected Successfully..."); 
    } 
    catch (SQLException e) 
    { 
     System.err.println(e); 

    } 
    finally 
    { 
     if (rs != null) 
     { 
      rs.close(); 
     } 
     if (st != null) 
     { 
      st.close(); 
     } 
     if (conn != null) 
     { 
      conn.close(); 
     } 
    } 
} 

}

---

Answer 1

錯誤類

import com.mysql.jdbc.Connection; 
import com.mysql.jdbc.Statement; 

應該

import java.sql.Connection; 
import java.sql.Statement; 

---

事實上，Java的解耦一切從一個特定的數據庫引擎。永遠不需要導入MySQL（或ProgressSQL或...）類。

要具有可這些類在運行時，在try後的第一件事，得到連接之前將是：

Class.forName("com.mysql.jdbc.Driver"); 

該技術將允許讀取從配置文件中的所有字符串，並寫入數據庫獨立的代碼。

---

缺少：康恩= ...

conn = DriverManager.getConnection(CONN_STR, userName, userpwd); 

Answer 2

package com.example.demo; 

import java.sql.*; 


public class DBConnect 
{ 
private static final String userName = "root"; 
private static final String userpwd = "sverma"; 
private static final String CONN_STR = "jdbc:mysql://localhost:3306/phpweb_db"; 

public static void main(String[] args) throws SQLException 
{ 

    Connection conn; 
    Statement st; 
    ResultSet rs; 

    try 
    { 
     Class.forName("com.mysql.jdbc.Driver"); 
     DriverManager.getConnection(CONN_STR, userName, userpwd); 
     st=conn.createStatement(ResultSet.TYPE_SCROLL_INSENSITIVE,ResultSet.CONCUR_READ_ONLY); 
     rs = st.executeQuery("select * from user"); 
     rs.last(); 
     System.out.println("No of rows: " + rs.getRow()); 

     // System.out.println("Connected Successfully..."); 
    } 
    catch (SQLException e) 
    { 
     System.err.println(e); 

    } 
    finally 
    { 
     if (rs != null) 
     { 
      rs.close(); 
     } 
     if (st != null) 
     { 
      st.close(); 
     } 
     if (conn != null) 
     { 
      conn.close(); 
     } 
    } 
}