JTree Problem

Of course - but who is writing this program? The map exists only while you are building the tree - it is then garbage collected. I do not beleive you are so short of memory.

Basically the problem is that you need to find the entry to attach to - the parent. You could keep the previouos parent and see if it's the right one (and then search its parent, etc - pretty painful), or search the entire tree looking for the parent. But this is swapping computational complexity for memory - a poor swap (since I started programming, computers have become a million times faster. As I have not, I tend towards solutions that make the computer work harder, rather than me).

The Map is a decent solution and using memory but fleetingly.

If you want to be sure it is indeed garbage collected:

public class Test4
    extends MyWindow {
  JTree tree;

  public Test4() {
    super("Creating a Simple JTree");

    String[] hierarchy = {
        "javax.swing", "javax.swing.border", "javax.swing.colorchooser", "javax.swing.event", "javax.swing.filechooser",
        "javax.swing.plaf", "javax.swing.plaf.basic", "javax.swing.plaf.metal", "javax.swing.plaf.multi",
        "javax.swing.table", "javax.swing.text", "javax.swing.text.html", "javax.swing.text.html.parser",
        "javax.swing.text.rtf", "javax.swing.tree", "javax.swing.undo"};

    DefaultMutableTreeNode root = new DefaultMutableTreeNode("packages", true);
    Map map = new HashMap();

    for (int i = 0; i < hierarchy.length; i++) {
      getList(hierarchy[i], root, map);
    }
    tree = new JTree(root);

    c.add(new JScrollPane(tree), BorderLayout.CENTER);
    setVisible(true);
  }

  public void getList(String s, DefaultMutableTreeNode root, Map map) {
    String[] x = s.split("\\.");

    DefaultMutableTreeNode parent = null;
    String fullname = ".";
    for (int i = 0; i < x.length; i++) {
      if (i == 0) {
        parent = root;
        fullname = x[0];
      } else {
        parent = (DefaultMutableTreeNode) map.get(fullname);
        fullname += "." + x[i];
      }

      DefaultMutableTreeNode node = new DefaultMutableTreeNode(x[i]);

      if (parent != null) {
        if (!map.containsKey(fullname)) {
          parent.add(node);
          map.put(fullname, node);
        }
      }
    }
  }

  public static void main(String[] args) {
    new Test4();
  }
}