title: "AWT-EventQueue-0" java.lang.NullPointerException - need some advices
body: <p>i'm new in Java World. I'm trying to create a simple app, populating a JTable from a local database. I have some issues with this error (shown below) and I can't realize what's going on...</p>
  
  <p>Error:</p>
  
  <pre><code>Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
  at ProiectDealerAuto.SwingInterface.Button4ActionPerformed(SwingInterface.java:231)
  at ProiectDealerAuto.SwingInterface.access$200(SwingInterface.java:22)
  at ProiectDealerAuto.SwingInterface$3.actionPerformed(SwingInterface.java:97)
  at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2022)
  at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2346)
  at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:402)
  at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:259)
  at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:252)
  at java.awt.Component.processMouseEvent(Component.java:6527)
  at javax.swing.JComponent.processMouseEvent(JComponent.java:3321)
  at java.awt.Component.processEvent(Component.java:6292)
  at java.awt.Container.processEvent(Container.java:2234)
  at java.awt.Component.dispatchEventImpl(Component.java:4883)
  at java.awt.Container.dispatchEventImpl(Container.java:2292)
  at java.awt.Component.dispatchEvent(Component.java:4705)
  at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4898)
  at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4533)
  at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4462)
  at java.awt.Container.dispatchEventImpl(Container.java:2278)
  at java.awt.Window.dispatchEventImpl(Window.java:2739)
  at java.awt.Component.dispatchEvent(Component.java:4705)
  at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:746)
  at java.awt.EventQueue.access$400(EventQueue.java:97)
  at java.awt.EventQueue$3.run(EventQueue.java:697)
  at java.awt.EventQueue$3.run(EventQueue.java:691)
  at java.security.AccessController.doPrivileged(Native Method)
  at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:75)
  at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:86)
  at java.awt.EventQueue$4.run(EventQueue.java:719)
  at java.awt.EventQueue$4.run(EventQueue.java:717)
  at java.security.AccessController.doPrivileged(Native Method)
  at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:75)
  at java.awt.EventQueue.dispatchEvent(EventQueue.java:716)
  at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:201)
  at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:116)
  at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:105)
  at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:101)
  at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:93)
  at java.awt.EventDispatchThread.run(EventDispatchThread.java:82)
  </code></pre>
  
  <p>I want to populate JTable when i press a button. This is the try-catch block for my button.</p>
  
  <pre><code>Connection connection = null;
      Statement statement = null;
  
  
      try{
  
       Class.forName("com.mysql.jdbc.Driver");
       connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/dealerauto","cosmin","kilimanjaro");
          ResultSet result = statement.executeQuery("SELECT * FROM cars");
          ResultSetMetaData rsmetadata = result.getMetaData();
          int coloumns = rsmetadata.getColumnCount();
          DefaultTableModel dtm = new DefaultTableModel();
          Vector coloumns_name = new Vector();
          Vector data_rows = new Vector();
  
          for (int i=1; i &lt; coloumns; i++)
          {
              coloumns_name.addElement(rsmetadata.getColumnName(i));
          }
          dtm.setColumnIdentifiers(coloumns_name);
          while(result.next())
          {
              data_rows = new Vector();
              for(int j=1; j&lt;coloumns; j++)
              {
                  data_rows.addElement(result.getString(j));
             }
              dtm.addRow(data_rows);
          }
  
          tbCars.setModel(dtm);
  
  
      }
        catch(ClassNotFoundException error)
     {
       System.out.println("Error "+ error.getMessage());
     }
      catch(SQLException error){
          System.out.println("Error "+ error.getMessage());
      }
  </code></pre>