Java SE (Java Platform, Standard Edition)

Hi, I have a JTree with custom model. I test it with the following structure:

+root
----+category
---------+file

When the app starts, root and category are visible, file is hidden. When I try to expand the category node, the whole JTree disappears. Any further clicks in the place previously occupied by the JTree result in a java.lang.NullPointerException at javax.swing.plaf.basic.BasicTreeUI$Handler.handleSelection().

The nodes I use represent a simple tree, where every node has its value and a LinkedList of its children. The model simply translates this to the "language" of TreeModel.

It is essential for me to correctly define equals() and hashCode() for the nodes. I found out that if the nodes' hashCode() doesn't rely on its list of children, everything works well. But I want it to rely on the children!

I use JRE 1.6.0_22 on Win7.

Where do I do something wrong, please?

Thanks very much for any help ;)

PS: I managed to workaround this - in a TreeSelectionListener I call tree.setModel(tree.getModel()) and then I restore the expanded and selected nodes. This works, but of course I'd rather have a cleaner solution. Moreover, this seems as a bug in JRE for me.

SSCCE included:

import java.awt.Dimension;
import java.util.LinkedList;
import java.util.List;

import javax.swing.JFrame;
import javax.swing.JTree;
import javax.swing.SwingUtilities;
import javax.swing.WindowConstants;
import javax.swing.event.TreeModelEvent;
import javax.swing.event.TreeModelListener;
import javax.swing.tree.TreeModel;
import javax.swing.tree.TreePath;

public class JTreeTest
{
    public static void main(String[] args)
    {
        // setup the tree
        final File list = new File();
        list.setValue("root");

        File category = new File();
        list.getFiles().add(category);
        category.setValue("category");

        File file = new File();
        category.getFiles().add(file);
        file.setValue("file");

        SwingUtilities.invokeLater(new Runnable() {
            @Override
            public void run()
            {
                JFrame frame = new JFrame();

                // setup the JTree
                JTree tree = new JTree(new MyModel(list));
                frame.add(tree);

                frame.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
                frame.setSize(new Dimension(200, 100));
                frame.setVisible(true);
            }
        });
    }

    // this model is very very basic and I don't see much space here for errors...
    static class MyModel implements TreeModel
    {
        protected File                    root;

        protected List<TreeModelListener> treeModelListeners = new LinkedList<TreeModelListener>();

        public MyModel(File root)
        {
            this.root = root;
        }

        @Override
        public File getRoot()
        {
            return root;
        }

        @Override
        public Object getChild(Object parent, int index)
        {
            if (index < 0)
                return null;

            if (!(parent instanceof File))
                return null;

            File fParent = (File) parent;

            try {
                return fParent.getFiles().get(index);
            } catch (ArrayIndexOutOfBoundsException e) {
                return null;
            }
        }

        @Override
        public int getChildCount(Object parent)
        {
            if (!(parent instanceof File))
                return 0;

            File fParent = (File) parent;

            return fParent.getFiles().size();
        }

        @Override
        public boolean isLeaf(Object node)
        {
            return getChildCount(node) == 0;
        }

        @Override
        public void valueForPathChanged(TreePath path, Object newValue)
        {
            if (!(newValue instanceof File))
                return;

            if (path.getParentPath() == null) {
                fireTreeNodesChanged(new TreeModelEvent(this, path, null, null));
            } else {
                fireTreeNodesChanged(new TreeModelEvent(this, path.getParentPath(), new int[] { getIndexOfChild(path
                        .getParentPath().getLastPathComponent(), newValue) }, new Object[] { newValue }));
            }
        }

        @Override
        public int getIndexOfChild(Object parent, Object child)
        {
            if (parent == null || child == null)
                return -1;

            if (!(parent instanceof File) || !(child instanceof File))
                return -1;

            File fParent = (File) parent;

            return fParent.getFiles().indexOf(child);
        }

        @Override
        public void addTreeModelListener(TreeModelListener l)
        {
            treeModelListeners.add(l);
        }

        @Override
        public void removeTreeModelListener(TreeModelListener l)
        {
            treeModelListeners.remove(l);
        }

        public void fireTreeNodesChanged(TreeModelEvent e)
        {
            for (TreeModelListener listener : treeModelListeners) {
                listener.treeNodesChanged(e);
            }
        }
    }

    static class File
    {
        static int fileId = 0;
        int        id;
        List<File> files  = null;
        String     value  = null;

        public File()
        {
            // ensure each item will have a really unique identifier, so no equals() collisions should occur
            id = fileId++;
        }

        public List<File> getFiles()
        {
            if (files == null)
                files = new LinkedList<File>();
            return files;
        }

        public String getValue()
        {
            return value;
        }

        public void setValue(String value)
        {
            this.value = value;
        }

        // generated by Eclipse code helpers
        @Override
        public int hashCode()
        {
            final int prime = 31;
            int result = 1;
            result = prime * result + ((value == null) ? 0 : value.hashCode());
            // ///////HERE IT IS////////
            // if you uncomment the following line, the list will get empty when you expand the second category and
            // any following clicks in any place that should be occupied by an item will result in a
            // NullPointerException
            //
            result = prime * result + ((files == null) ? 0 : files.hashCode());
            //
            result = prime * result + id;
            return result;
        }

        @Override
        public boolean equals(Object obj)
        {
            if (this == obj)
                return true;
            if (obj == null)
                return false;
            if (getClass() != obj.getClass())
                return false;
            File other = (File) obj;
            if (value == null) {
                if (other.value != null)
                    return false;
            } else if (!value.equals(other.value))
                return false;
            if (files == null) {
                if (other.files != null)
                    return false;
            } else if (!files.equals(other.files))
                return false;
            if (id != other.id)
                return false;
            return true;
        }

        @Override
        public String toString()
        {
            return "File [value=" + value + "]";
        }
    }

}