Tooltip Null Pointer

[Isaac Hewitt]

This exception thrown is what I get ' occasionally ' when the mouse is passed over my JTable. I have tried testing every which way for a null pointer with the method below and cannot find what it is. The second method was added recently but the exception has nothing to do with it - (exception was thrown before this addition) See exception code further down.

    @Override
    public String getToolTipText(MouseEvent e) {
        
          final Point p = e.getPoint();
  
          final int col = this.columnAtPoint(p);
          
          final int row = this.rowAtPoint(p);
          
          String data = null;
          
          if((col >= 0) && (row >= 0)) {
              
              if(MyPreferences.getInt("table_row") == 0) { //JUST GET DATA FROM SINGLE CELL
                  
              final Object ob = this.getValueAt(row, col);
           
              return ob.toString();
              
              } else {
                  
                  data = this.getTableRowData(row);
                
              }
          }
          
          return data.toString();
    }


    private String getTableRowData(int row) {
        
       final StringBuilder b = new StringBuilder();
                  
       for(int j = 0; j < 6; j++) {
                      
          if(j == 4) {
             b.append(this.getValueAt(row, j));
             b.append("m.     ");
          } else {
             b.append(this.getValueAt(row, j));
          }
                      
          if(j == 4) {
              continue;
          }
                      
          if(j == 5) {
              break;
          }
                      
          b.append("      ");
                      
    }
                  
       return b.toString();
        
    }

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at film_titles.table.Table.getToolTipText(Unknown Source)
at javax.swing.ToolTipManager.checkForTipChange(ToolTipManager.java:589)
at javax.swing.ToolTipManager.mouseMoved(ToolTipManager.java:561)
at java.awt.AWTEventMulticaster.mouseMoved(AWTEventMulticaster.java:330)
at java.awt.Component.processMouseMotionEvent(Component.java:6549)
at javax.swing.JComponent.processMouseMotionEvent(JComponent.java:3339)
at java.awt.Component.processEvent(Component.java:6273)
at java.awt.Container.processEvent(Container.java:2229)
at java.awt.Component.dispatchEventImpl(Component.java:4860)
at java.awt.Container.dispatchEventImpl(Container.java:2287)
at java.awt.Component.dispatchEvent(Component.java:4686)
at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4832)
at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4505)
at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4422)
at java.awt.Container.dispatchEventImpl(Container.java:2273)
at java.awt.Window.dispatchEventImpl(Window.java:2713)
at java.awt.Component.dispatchEvent(Component.java:4686)
at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:707)
at java.awt.EventQueue.access$000(EventQueue.java:101)
at java.awt.EventQueue$3.run(EventQueue.java:666)
at java.awt.EventQueue$3.run(EventQueue.java:664)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:87)
at java.awt.EventQueue$4.run(EventQueue.java:680)
at java.awt.EventQueue$4.run(EventQueue.java:678)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:677)
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:211)
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:128)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:117)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:113)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:105)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:90)

[Rob Spoor]

The exception is thrown directly from your own getToolTipText method. That means that inside that method, a null reference is dereferenced. Since neither e nor this will be null, that leaves two culprits (assuming the MyPreferences.getInt method is static):
1) ob is null when calling toString() on it.
2) data is null when calling toString() on it.