從Jtable更新數據庫行：錯誤

Question

我得到了一個jTable，當應用程序運行時，它將其填充數據庫項目。現在我已經創建了一個保存按鈕，它可以修改這些更改並將其保存到數據庫中，但我一直收到一個我無法弄清楚的錯誤。

按鈕：

private void btnOpslaanActionPerformed(java.awt.event.ActionEvent evt) { 
     // TODO add your handling code here: 
     int row = jTable1.getSelectedRow(); 
     int col = jTable1.getSelectedColumn(); 

     int category_id = (Integer)(jTable1.getValueAt(row, 1)); 
     String name = jTable1.getValueAt(row, 2).toString(); 
     double price = (Double)jTable1.getValueAt(row, 3); 
     String description = jTable1.getValueAt(row, 4).toString(); 

     queryManager.updateProductList(category_id, name, price, description); 
    } 

與系統了（所以這是工作的罰款） 我得到了這條線的誤差測試的更新變量：

queryManager.updateProductList(category_id, name, price, description); 

queryManager.updateProductList方法：

public void updateProductList(int category_id, String name, double price, String description){ 
     String sql ="UPDATE product SET categorie_id='" +category_id+ "', naam='" +name+ "', prijs='" +price+ "', omschrijving='"+description+"'"; 
     ResultSet result = dbmanager.doQuery(sql); 
     try { 
      result.next(); 
     } catch (SQLException e) { 
      System.out.println("Productlijst updaten is niet gelukt: " + e.getMessage()); 
     } 

    } 

希望任何人都可以幫助我這個pr oblem！此外，我得到的錯誤：

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException 
    at view.ShowProductList.btnOpslaanActionPerformed(ShowProductList.java:162) 
    at view.ShowProductList.access$400(ShowProductList.java:19) 
    at view.ShowProductList$6.actionPerformed(ShowProductList.java:108) 
    at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2028) 
    at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2351) 
    at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:387) 
    at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:242) 
    at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:236) 
    at java.awt.Component.processMouseEvent(Component.java:6382) 
    at javax.swing.JComponent.processMouseEvent(JComponent.java:3275) 
    at java.awt.Component.processEvent(Component.java:6147) 
    at java.awt.Container.processEvent(Container.java:2083) 
    at java.awt.Component.dispatchEventImpl(Component.java:4744) 
    at java.awt.Container.dispatchEventImpl(Container.java:2141) 
    at java.awt.Component.dispatchEvent(Component.java:4572) 
    at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4619) 
    at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4280) 
    at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4210) 
    at java.awt.Container.dispatchEventImpl(Container.java:2127) 
    at java.awt.Window.dispatchEventImpl(Window.java:2489) 
    at java.awt.Component.dispatchEvent(Component.java:4572) 
    at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:704) 
    at java.awt.EventQueue.access$400(EventQueue.java:82) 
    at java.awt.EventQueue$2.run(EventQueue.java:663) 
    at java.awt.EventQueue$2.run(EventQueue.java:661) 
    at java.security.AccessController.doPrivileged(Native Method) 
    at java.security.AccessControlContext$1.doIntersectionPrivilege(AccessControlContext.java:87) 
    at java.security.AccessControlContext$1.doIntersectionPrivilege(AccessControlContext.java:98) 
    at java.awt.EventQueue$3.run(EventQueue.java:677) 
    at java.awt.EventQueue$3.run(EventQueue.java:675) 
    at java.security.AccessController.doPrivileged(Native Method) 
    at java.security.AccessControlContext$1.doIntersectionPrivilege(AccessControlContext.java:87) 
    at java.awt.EventQueue.dispatchEvent(EventQueue.java:674) 
    at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:296) 
    at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:211) 
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:201) 
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:196) 
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:188) 
    at java.awt.EventDispatchThread.run(EventDispatchThread.java:122) 

Answer 1

可能「queryManager」未正確istantiated。 您是否嘗試過調試您的代碼？