How to solve the tree update problem

Question

Hi all,
I met a urgent problem, I defined two tree control over two JScrollPanes.
two JScrollPanes are in a JSplitPane which is located in another JSplit's left. The left JSplitPane and another JTextarea both are in another JSplitPane.they are layouted as:
JTree1 | JTextArea
JTree2 | JTextArea
I want to achieve this: when I clicked a node in JTree1,then JTree2 is changed in the viewport according to the content of the clicked node.
I use the following essential code :
public class TNTree extends JTree {
private TemplateFrame frame1;
public TNTree(TemplateFrame frame/*,XTree tree*/)
this.frame1=frame;
getSelectionModel().setSelectionMode(TreeSelectionModel.SINGLE_TREE_SELECTION);
setShowsRootHandles(true);
setEditable(false);
try{
treeModel=initTree();
setModel(treeModel);
jbInit();
}catch(Exception e){}
this.addMouseListener(new MouseAdapter(){
public void mouseClicked(MouseEvent e) {
TreePath tp=getPathForLocation(e.getX(), e.getY());
pt.x=e.getX();
pt.y=e.getY();
try{
if((e.getModifiers()&InputEvent.BUTTON1_MASK)==InputEvent.BUTTON1_MASK)
setSelectionPath(tp);
if(e.getClickCount()==1){
if((tp!=null)&&(!isIn((DefaultMutableTreeNode)tp.getLastPathComponent())))
{    tempStr=((DefaultMutableTreeNode)tp.getLastPathComponent()).toString();
Connection con=getConnection();
PreparedStatement pstmt;
pstmt=con.prepareStatement("select content from template ,tcontent"+
" where template.tcode=tcontent.tcode and name=?");
pstmt.setString(1,tempStr);
ResultSet rset=pstmt.executeQuery();
String str="";
if(rset.next()){
str=rset.getString(1);
treeStr=str;
System.out.println(treeStr);
// frame1.xTree =new XTree(frame1,str);
// frame1.xTree=new XTree(frame1);
frame1.xTree.refresh( str );
frame1.jScroll.getViewport().add(frame1.xTree);
// frame1.repaint();
if(e.getClickCount()==2){
}else
}catch(Exception e1){e1.printStackTrace();}
public class XTree extends JTree {
private TemplateFrame frame;
public XTree(TemplateFrame frame) throws ParserConfigurationException
this.frame=frame;
refreshTextFlag=false;
strBuffer=new StringBuffer();
     getSelectionModel().setSelectionMode( TreeSelectionModel.SINGLE_TREE_SELECTION );
     setShowsRootHandles( true );
     setEditable( false );
     dbf = DocumentBuilderFactory.newInstance();
     dbf.setValidating( false );
     db = dbf.newDocumentBuilder();
treeModel = buildWelcomeTree();
setModel(treeModel );
TreeTXT = "";
try{
jbInit();
catch(Exception e){
//e.printStackTrace();
Error err = new Error();
eBuffer.append(err.getValue("Err#4"));
eBuffer.append("\r\n");
public void refresh( String text ) //throws ParserConfigurationException
try{
treeModel=buildTree(text);
setModel( treeModel );
TreeTXT = text;
}catch(Exception e){
// e.printStackTrace();
Error err = new Error();
eBuffer.append(err.getValue("Err#1"));
eBuffer.append("\r\n");
public class TemplateFrame extends JFrame
static XTree xTree=null;
static TNTree tnTree;
xTree=new XTree(this);
tnTree=new TNTree(this);
jScrollLeft.getViewport().add(tnTree);
void fileOpen_ActionPerformed(ActionEvent e)
String fileName = "";
BufferedReader reader;
String line;
StringBuffer xmlText;
JFileChooser chooser = new JFileChooser();
Container parent = jMenuItem4.getParent();
int choice = chooser.showOpenDialog(parent);
int returnVal = chooser.showOpenDialog(this);
if(returnVal == JFileChooser.APPROVE_OPTION) {
textMessage.setText("You chose to open this file: " +
chooser.getSelectedFile().getAbsolutePath() );
// chooser.getSelectedFile().getName());
fileName = chooser.getSelectedFile().getAbsolutePath();
path=fileName;
if(fileName.substring(fileName.length()-3,fileName.length()).equalsIgnoreCase("xml"))
//Will fix future
try{
reader = new BufferedReader( new FileReader( fileName ) );
xmlText = new StringBuffer();
while ( ( line = reader.readLine() ) != null )
xmlText.append( line+"\n" );
reader.close();
//refresh the xml tree
xTree.refresh( xmlText.toString() );
textArea.setText( xmlText.toString() ) ;
/*Set the title*/
//fTitle = chooser.getSelectedFile().getName();
fTitle = chooser.getSelectedFile().getName();
this.setTitle(fTitle/*+mTitle */ );
//Sign the editor has a file
dirty = true;
}catch(Exception Mye) {
textMessage.setText("Error occured when opening the file");
}else{
textMessage.setText("Error occured when the opening file is not a xml file");
Now my problem is when in TemplateFrame cl*** I call open method including import xTree.refresh(string),I can get the right results ,the JTree2 is refreshed correctly,but when in TNTree cl*** I call the xTree.refresh(String),I met a java.lang.nullpointer exception , How can I solve this problem?
Are there other better ways to slove this problem?

Answer 1

Hm ...
what should it be otherwise?- You said, the problem is calling frame1.xTree.refresh(str) - and the NullPointerException is thrown there - so there are only 2 possibilities - frame1 is null or xTree is null. So please add the following code before this line ...
if (frame1==null) { System.out.println("frame1 is null"); }
else if (frame1.xTree==null) { System.out.println("frame1.xTree is null"); }
else System.out.println("None of them is null - I haven't read the runtime error correctly");and then you will see, where the problem is :)
greetings Marsian