Problems in creating a preorder tree node arraylist

Question

Hi, i want to create an arraylist containing a preorder tree node's name, the program compiled well but every time it gives error when i press the "Output Preorder" button to create the arraylist, the following is the code, can someone help? Thanks a lot!!
                JButton outputPreorderButton = new JButton("Output Preorder");
outputPreorderButton.addActionListener(new ActionListener()
     public void actionPerformed(ActionEvent e)
        for (Enumeration evev = tableTreeRootNode.preorderEnumeration() ; evev.hasMoreElements() ;) {
               System.out.println(evev.nextElement());
               String s = (String)evev.nextElement();
               tableTreeNodesArray.add(s);

Answer 1

Yeah, well, it will "give error" (as you so precisely and informatively say) if there's an odd number of nodes in your tree. Consider your code:System.out.println(evev.nextElement());
// Get element number 1 and print it.
String s = (String)evev.nextElement();
tableTreeNodesArray.add(s);
// Get element number 2 and add it to the list.So, the odd-numbered elements you print. The even-numbered elements you add to the list. If it happens there are 31 nodes, then an error will occur when you try to get node 32.