java：不能从静态上下文中引用非静态变量错误

Question

以下代码在变量上产生了错误，con2说 "non-static variable con2 cannot be referenced from a static context Error."我用Google搜索解决方案，并且他们暗示尚未初始化该变量以使方法可用。我初始化不正确吗？我也尝试过将事情改为公开，但这也无济于事。

import java.io.*;
import java.net.*;

import java.sql.*;
import java.sql.CallableStatement;
import java.sql.ResultSet;
import java.sql.PreparedStatement;
import net.sourceforge.jtds.jdbcx.JtdsDataSource;
import net.sourceforge.jtds.jdbc.Driver;

class testconnect { 

     private java.sql.Connection con2 = null;

     private final String url2 = "jdbc:jtds:sqlserver://";
     private final String serverName= "SQL01";
     private final String portNumber = "2677";
     private final String databaseName= "App";
     private final String userName = "bob";
     private final String password = "boob";
     private final String selectMethod = "cursor";  

     private String getConnectionUrl2(){
        System.out.println("initalizing jtds");
          //String returnVal = url+serverName+":"+portNumber+";databaseName="+databaseName+";user="+userName+";password="+password+";instance="+instance+";";
          String returnVal = url2+serverName+":"+portNumber+"/"+databaseName+";user="+userName+";password="+password;
          System.out.println("url2: " + returnVal);
          return returnVal;
     }

     public static void main (String[] args) { 
         con2 = java.sql.DriverManager.getConnection(getConnectionUrl2());

     } 

} //end class 

Answer 1

不，实际上，你必须声明con2字段为静态：

private static java.sql.Connection con2 = null;

编辑：更正，实际上是远远不够的，你将遇到相同的问题，因为getConnection2Url方法也不是静态的。更好的解决方案可能是改为进行以下更改：

 public static void main (String[] args) { 
     new testconnect().run();
 } 

 public void run() {
     con2 = java.sql.DriverManager.getConnection(getConnectionUrl2());
 }