选课.java

经过调查分析

          if(flag!=0)
              {
               String sql1="delete from 成绩 where 学号='"+studentNumber+"' AND 课程号='"+number+"'";
               int reg= statement.executeUpdate(sql1);
               if(reg==1)    
               {JOptionPane.showMessageDialog(null,"成功删除课程！");
                 jTextArea1.setText("");
               }
              }
            if(flag==0)
            JOptionPane.showMessageDialog(null,"输入课程号错误或您没有选这门课程！");    
                  
        }
        
        
        catch(SQLException sqlException){
        JOptionPane.showMessageDialog(null,sqlException.getMessage(),"Database Error",JOptionPane.ERROR_MESSAGE);
        System.exit(1);}

       catch(ClassNotFoundException classNotFound){
       JOptionPane.showMessageDialog(null,classNotFound.getMessage(),"Driver Not Found",JOptionPane.ERROR_MESSAGE);
        System.exit(1); }
   // TODO add your handling code here:
    }//GEN-LAST:event_jButton2ActionPerformed

    private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) {//GEN-FIRST:event_jButton1ActionPerformed
    
        
        Statement statement;
        String number=new String(jTextField1.getText());
        int flag0=0;
        
         try{
                Connect con=new Connect();
                statement=con.con.createStatement();
                
                String sql="select 选课状态 from 课程 where 选课属性='选修'";
                ResultSet resultSet0=statement.executeQuery(sql);
                while(resultSet0.next()){
                   if(resultSet0.getObject(1).toString().equals("开通"))
                   {  flag0=1;
                      break;
                   }     
                 }
                
                
                if(flag0==0)
                  JOptionPane.showMessageDialog(null,"暂未开通选课！");   
               
                if(flag0==1)
                { 
               
                String s1="必修",s2=null;
                int flag=0 ;
                s2="SELECT 选课属性 FROM 课程 WHERE 课程号='"+number+"'";
                
                ResultSet resultSet=statement.executeQuery(s2);
                ResultSetMetaData metaData=resultSet.getMetaData();
                int numberOfColumns=metaData.getColumnCount();
                
                while(resultSet.next()){
                    for(int i=1;i<=numberOfColumns;i++)
                    { 
                       if(s1.equals(resultSet.getObject(i).toString()))
                          { 
                           
                            flag=0;
                            break;
                        }
                        else flag=1;
                    }
                 }
                
                if(flag==0)
                    JOptionPane.showMessageDialog(null,"该课程为必修或输入课程号有误，请重新选课！");
                
                
                if(flag==1) 
               { 
                 
                String str,studentNumber = null;
                
                str="SELECT 编号 FROM 用户 WHERE 状态='登录'";
                
                ResultSet resultSet1=statement.executeQuery(str);
                ResultSetMetaData metaData1=resultSet1.getMetaData();
                int numberOfColumns1=metaData1.getColumnCount();
                
                while(resultSet1.next()){
                    for(int i=1;i<=numberOfColumns1;i++)
                        studentNumber=resultSet1.getObject(i).toString();
                     }
                
                String str1,str2,renshu1=null,renshu2=null;
                int a,b;
                
                str1="SELECT 限选人数 FROM 课程 WHERE 课程号='"+number+"'";
                
                ResultSet resultSet2=statement.executeQuery(str1);
                ResultSetMetaData metaData2=resultSet2.getMetaData();
                int numberOfColumns2=metaData2.getColumnCount();
                
                while(resultSet2.next()){
                    for(int i=1;i<=numberOfColumns2;i++)
                        renshu1=resultSet2.getObject(i).toString();
                     }
               a=Integer.parseInt(renshu1);
               
               str2="SELECT 已选人数 FROM 课程 WHERE 课程号='"+number+"'";
                
                ResultSet resultSet3=statement.executeQuery(str2);
                ResultSetMetaData metaData3=resultSet3.getMetaData();
                int numberOfColumns3=metaData3.getColumnCount();
                
                while(resultSet3.next()){
                    for(int i=1;i<=numberOfColumns3;i++)
                        renshu2=resultSet3.getObject(i).toString();
                     }
               b=Integer.parseInt(renshu2);
               
               if(a>b)
                 { 
                    String str3=null,str4=null;
                    b++;
                    
                   
                    
                    str3="insert into 成绩 values('"+studentNumber+"','"+number+"',null)";
                    int reg=0;
                   reg=statement.executeUpdate(str3);
                   
                   String str5=Integer.toString(b); 
                    
                   str4="UPDATE 课程 SET 已选人数='"+str5+"'WHERE 课程号='"+number+"'";
                   reg=statement.executeUpdate(str4);
                   
                  
                  
                  
                 
                   StringBuffer results=new StringBuffer();
                   results.append("       已选课程    ");
                   results.append("\n\n");
                   
                   ResultSet resultSet4=statement.executeQuery("select * from 课程 where 课程号='"+number+"'");
                   ResultSetMetaData metaData4=resultSet4.getMetaData();
                   int numberOfColumns4=metaData4.getColumnCount();
                
                   for(int i=1;i<=numberOfColumns4;i++)
                    results.append(metaData4.getColumnName(i)+"\t");
                
                results.append("\n");
                
                while(resultSet4.next()){
                    for(int i=1;i<=numberOfColumns4;i++)
                         results.append(resultSet4.getObject(i)+"\t");
                     results.append("\n");
                     }
                
                   jTextArea1.setText(results.toString());
                   jTextArea1.setEditable(false);
                 
                 
                }
             else
                JOptionPane.showMessageDialog(null,"选课人数已满，请选其它课程！");
            }
       } 
      
 }


    catch(SQLException sqlException){
        JOptionPane.showMessageDialog(null,sqlException.getMessage(),"Database Error",JOptionPane.ERROR_MESSAGE);
        System.exit(1);}

   catch(ClassNotFoundException classNotFound){
       JOptionPane.showMessageDialog(null,classNotFound.getMessage(),"Driver Not Found",JOptionPane.ERROR_MESSAGE);
        System.exit(1); }
       
   // TODO add your handling code here:
    }//GEN-LAST:event_jButton1ActionPerformed
    
    
    // Variables declaration - do not modify//GEN-BEGIN:variables
    private javax.swing.JButton jButton1;
    private javax.swing.JButton jButton2;
    private javax.swing.JButton jButton3;
    private javax.swing.JLabel jLabel1;
    private javax.swing.JLabel jLabel2;
    private javax.swing.JScrollPane jScrollPane1;
    private javax.swing.JScrollPane jScrollPane2;
    private javax.swing.JTextArea jTextArea1;
    private javax.swing.JTextArea jTextArea2;
    private javax.swing.JTextField jTextField1;
    // End of variables declaration//GEN-END:variables
    
}