add a alert message on timestep tab:

when user set focus in the source time lag field, a window pop up to warn "non-negative number"

gui/src/de/mpg/mpimet/yacgui/ui/dialog/tabpanel/TimestepTab.java

@@ -8,9 +8,12 @@ import javax.swing.BoxLayout;
 import javax.swing.JComboBox;
 import javax.swing.JFormattedTextField;
 import javax.swing.JFormattedTextField.AbstractFormatter;
+import javax.swing.JFrame;
 import javax.swing.JLabel;
+import javax.swing.JOptionPane;
 import javax.swing.JPanel;
 import javax.swing.JTextField;
+import javax.swing.JWindow;
 import javax.swing.border.EmptyBorder;
 import javax.swing.text.DefaultFormatter;
 import javax.swing.text.DefaultFormatterFactory;
@@ -19,6 +22,15 @@ import javax.swing.text.InternationalFormatter;
 import javax.swing.text.MaskFormatter;
 import javax.swing.text.NumberFormatter;
 
+
+import java.awt.event.FocusEvent;
+import java.awt.event.FocusListener;
+
+import java.awt.GridLayout;
+import java.awt.MouseInfo;
+import java.awt.event.MouseEvent;
+import java.awt.event.MouseListener;
+
 import de.mpg.mpimet.yacgui.xml.CouplingOperation;
 //import de.mpg.mpimet.yacgui.xml.Timelag;
 import de.mpg.mpimet.yacgui.xml.Timestep;
@@ -167,9 +179,92 @@ public class TimestepTab extends AbstractTab {
 		});
 		sourceTimeLagInputField.setColumns(DEFAULT_COLUMN_NUM);
 		sourceTimeLagInputField.setHorizontalAlignment(JTextField.RIGHT);
+		
+		/**
+		 * pop up a window "non-negative number" when user set focus in the field
+		 */
+		sourceTimeLagInputField.addFocusListener(new FocusListener() {
+			
+			  JWindow jw =new JWindow();
+
+		      public void focusGained(FocusEvent e) {
+		        displayMessage("non-negative number", e);
+		      }
+
+		      public void focusLost(FocusEvent e) {
+	               if(jw!=null)jw.setVisible(false);
+		      }
+
+		      void displayMessage(String prefix, FocusEvent e) {
+		    	  
+		    	   if(jw==null){
+					  jw =new JWindow();
+					  JWindow jw =new JWindow();
+					  // TODO Auto-generated method stub
+					  JLabel jwLabel= new JLabel("non-negative number"); 
+					  jwLabel.setBackground(sourceTimeLagPanel.getBackground());
+					  jw.setLayout(new GridLayout(1,1));
+					  jw.add(jwLabel);
+		    	   }
+                    
+				   jw.setLocation(MouseInfo.getPointerInfo().getLocation().x + 5, MouseInfo.getPointerInfo().getLocation().y + 5);
+				   jw.setAlwaysOnTop(true);
+				   jw.setSize(150, 30);
+				   jw.setVisible(true);
+		      }
+
+		    });
 		sourceTimeLagPanel.add(sourceTimeLagInputField);
 		sourceTimeLagPanel.add(new JLabel(TIMESTEP_UNIT_LABEL));
-
+		
+//		sourceTimeLagPanel.addMouseListener(new MouseListener(){
+//      	  		   
+//            JWindow jw=null;
+//
+//            @Override
+//            public void mouseExited(MouseEvent e) {
+//                    // TODO Auto-generated method stub
+//                if(jw!=null)jw.setVisible(false);
+//            }
+//
+//			@Override
+//			public void mouseClicked(MouseEvent arg0) {
+//				// TODO Auto-generated method stub
+//				
+//			}
+//
+//			@Override
+//			public void mousePressed(MouseEvent e) {
+//				// TODO Auto-generated method stub
+//				
+//			}
+//
+//			@Override
+//			public void mouseReleased(MouseEvent e) {
+//				// TODO Auto-generated method stub
+//				
+//			}
+//			
+//			@Override
+//	        public void mouseEntered(MouseEvent e) {
+//	                // TODO Auto-generated method stub
+//				   if(jw==null){
+//                       jw =new JWindow();
+//                       // TODO Auto-generated method stub
+//                       JLabel jwLabel= new JLabel("non-negative number"); 
+//                       jwLabel.setBackground(sourceTimeLagPanel.getBackground());
+//                       jw.setLayout(new GridLayout(1,1));
+//                       jw.add(jwLabel);
+//                   }
+//				     
+//				   jw.setLocation(MouseInfo.getPointerInfo().getLocation().x, MouseInfo.getPointerInfo().getLocation().y);
+//				   jw.setAlwaysOnTop(true);
+//				   jw.setSize(150, 30);
+//				   jw.setVisible(true);
+//	           }
+//	           
+//		});
+		
 		// target lag
 		JPanel targetTimeLagPanel = new JPanel();
 		targetTimeLagPanel.add(new JLabel("Target Time Lag: "));