連接對象的範圍jdbc中的Con

Question

*語法錯誤*

我正面臨着JDBC的問題。 在這一行：

Connection con =DriverManager.getConnection("jdbc:odbc:recordtbl","scott","tiger"); 

這裏在con錯誤出現，我重命名這個變量。

這是我的代碼：

package md5IntegrityCheck; 
import java.io.UnsupportedEncodingException; 
import java.security.NoSuchAlgorithmException; 
import java.util.Scanner; 

import java.sql.*; 
import java.awt.*; 
import java.awt.event.*; 
import javax.swing.*; 
public class MD5IntegrityCheck 
{ 

    public static void main(String[] args) 
    throws UnsupportedEncodingException, NoSuchAlgorithmException 
    { 


     Statement stmt; 
     ResultSet rs; 
     Connection con=null; 
     PreparedStatement pst=null; 
     try 
     { 
      Class.forName("sun.jdbc.odbc.JdbcOdbcDriver"); 
      Connection con =DriverManager.getConnection("jdbc:odbc:recordtbl","scott","tiger"); 
        } 
      catch(Exception ee) 
      {ee.printStackTrace();} 

      System.out.println("Step 1"); 
      System.out.println(con.isClosed()); 

      System.out.println("Enter the filename"); 
      Scanner scanner = new Scanner(System.in); 
      String filename=scanner.nextLine(); 
      String chksumno="somevalue2"; 


      // get the file name here and store it in filename variable; 
      MD5 md5 = new MD5(filename); 
      System.out.println("test"); 
      chksumno = md5.getHashValue(); 

      System.out.println("Step 2"); 
      try{ 
       Class.forName("sun.jdbc.odbc.JdbcOdbcDriver"); 
       con = DriverManager.getConnection("jdbc:odbc:recordtbl","scott","tiger"); 

       pst=con.prepareStatement("insert into recordtbl values(?,?)"); 

      //System.out.println(pst.isClosed()); 
      System.out.println("Step3"); 
      pst.setString(1,filename); 
      System.out.println("Step 4"); 
      pst.setString(2,chksumno); 
      System.out.println("Step 5"); 
      pst.execute(); 

      System.out.println("Statement was EXECUTED!"); 
      con.close(); 
      } 


      catch(Exception ee) 
      {ee.printStackTrace();} 


    if (args.length <= 0) 
    { 
     Md5Gui gui = new Md5Gui(); 
     gui.runGui(); 
    } 
    else 
    { 
     DoWork runningProgram = new DoWork(); 
     runningProgram.run(args); 
    } 
    } 
} 

Answer 1

你已經宣佈所謂con在您嘗試聲明它第二次範圍內的局部變量。這在Java中是不允許的。只要改變它，以便第二次它是一個分配的，而不是聲明：

con = DriverManager.getConnection("jdbc:odbc:recordtbl", "scott", "tiger"); 

（有各種其他的事情我會改變你的代碼，包括關閉連接等在finally塊，但是這應該解決您的眼前的問題。）