JAVA File Tree Model slow for pendrive
===

I'm developing an application which will work with external memories accessed through USB a lot.
I've implemented TreeModel for browsing directories o disks. It works great for:

 - local discs on Ubuntu
 - connected external memories on Ubuntu
 - local discs on Windows 7
 
, but it sucks for connected external memories on Windows 7 and I don't know why. Event scrolling a JTree with this model with pendrive as a root is very glitchy. At the beggining I've thought that `listFiles()` from java.io.File is slow for pendrive so I've added samo kind of caching to model but it didn't work - scrolling still sucks.

I've just noticed that it have something to do with Look&Feel. For system L&F on Windows it sucks BAD, for Nimbus L&F it is not that bad but still not perfect.

FileTreeModel:

    import java.io.File;
    import java.io.FileFilter;
    import java.io.Serializable;
    import java.util.*;
    import javax.swing.event.TreeModelEvent;
    import javax.swing.event.TreeModelListener;
    import javax.swing.tree.TreeModel;
    import javax.swing.tree.TreePath;
    
    public class FileTreeModel implements TreeModel {
    
        private File root;
        private boolean onlyFolders;
        private boolean showHidden;
        private final Object LEAF = new Serializable() {
        };
        private Map<File, Object> map;
        private LinkedList<TreeModelListener> listeners = new LinkedList<>();
        private FileFilter directoryFilter = new FileFilter() {
    
            @Override
            public boolean accept(java.io.File pathname) {
                return pathname.isDirectory();
            }
        };
    
        public FileTreeModel(File root, boolean onlyFolders, boolean showHidden) {
            this.root = root;
            this.onlyFolders = onlyFolders;
            this.showHidden = showHidden;
            this.map = new HashMap();
        }
    
        public FileTreeModel() {
        }
    
        public boolean isShowHidden() {
            return showHidden;
        }
    
        public void setShowHidden(boolean showHidden) {
            this.showHidden = showHidden;
        }
    
        @Override
        public Object getRoot() {
            return root;
        }
    
        public void setRoot(File root) {
            Object oldRoot = this.root;
            this.root = root;
            map.clear();
            TreeModelEvent event = new TreeModelEvent(root, new Object[]{root});
            for (TreeModelListener listener : listeners) {
                listener.treeStructureChanged(event);
            }
        }
    
        @Override
        public boolean isLeaf(Object node) {
            return ((File) node).isFile();
        }
    
        @Override
        public int getChildCount(Object parent) {
            if (parent instanceof java.io.File && ((java.io.File) parent).canRead()) {
                List<File> files = children(parent);
                int result = 0;
                for (java.io.File file : files) {
                    if (((file.isDirectory() && onlyFolders) || !onlyFolders)
                            && ((!file.isHidden() && !showHidden) || showHidden)) {
                        result++;
                    }
                }
                return result;
            }
            return 0;
        }
    
        @Override
        public Object getChild(Object parent, int index) {
            if (parent instanceof java.io.File) {
                List<File> files = children(parent);
                List<java.io.File> resultFiles = new LinkedList<>();
                for (java.io.File file : files) {
                    if (((file.isDirectory() && onlyFolders) || !onlyFolders)
                            && ((!file.isHidden() && !showHidden) || showHidden)) {
                        resultFiles.add(file);
                    }
                }
                return resultFiles.get(index);
            }
            return null;
        }
    
        @Override
        public int getIndexOfChild(Object parent, Object child) {
            if (parent instanceof java.io.File) {
                List<File> files = children(parent);
                List<java.io.File> resultFiles = new LinkedList<>();
                for (java.io.File file : files) {
                    if (((file.isDirectory() && onlyFolders) || !onlyFolders)
                            && ((!file.isHidden() && !showHidden) || showHidden)) {
                        resultFiles.add(file);
                    }
                }
                return resultFiles.indexOf(child);
            }
            return -1;
        }
    
        @Override
        public void valueForPathChanged(TreePath path, Object newvalue) {
        }
    
        @Override
        public void addTreeModelListener(TreeModelListener l) {
            listeners.add(l);
        }
    
        @Override
        public void removeTreeModelListener(TreeModelListener l) {
            listeners.remove(l);
        }
    
        //============================PRIVATE METHODS===============================
        protected List<File> children(Object node) {
            File f = (File) node;
            Object value = map.get(f);
            if (value == LEAF) {
                return null;
            }
            List children = (List) value;
            if (children == null) {
                File[] c = f.listFiles();
                if (c != null) {
                    children = new ArrayList(c.length);
                    for (int len = c.length, i = 0; i < len; i++) {
                        children.add(c[i]);
                        if (!c[i].isDirectory()) {
                            map.put(c[i], LEAF);
                        }
                    }
                } else {
                    children = new ArrayList(0);
                }
                map.put(f, children);
            }
            return children;
        }
    }

Sample form:

    import folderlist.model.treemodels.FileTreeModel;
    import java.io.File;
    import java.util.Vector;
    import javax.swing.DefaultComboBoxModel;
    
    public class NewJFrame extends javax.swing.JFrame {
    
        public NewJFrame() {
            initComponents();
        }
    
        @SuppressWarnings("unchecked")
        // <editor-fold defaultstate="collapsed" desc="Generated Code">
        private void initComponents() {
    
            jComboBox1 = new javax.swing.JComboBox();
            jButton1 = new javax.swing.JButton();
            jScrollPane1 = new javax.swing.JScrollPane();
            jTree1 = new javax.swing.JTree();
    
            setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);
    
            jComboBox1.addActionListener(new java.awt.event.ActionListener() {
                public void actionPerformed(java.awt.event.ActionEvent evt) {
                    jComboBox1ActionPerformed(evt);
                }
            });
    
            jButton1.setText("Refresh");
            jButton1.addActionListener(new java.awt.event.ActionListener() {
                public void actionPerformed(java.awt.event.ActionEvent evt) {
                    jButton1ActionPerformed(evt);
                }
            });
    
            jTree1.setModel(new FileTreeModel());
            jScrollPane1.setViewportView(jTree1);
    
            javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane());
            getContentPane().setLayout(layout);
            layout.setHorizontalGroup(
                layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                .addGroup(layout.createSequentialGroup()
                    .addContainerGap()
                    .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                        .addGroup(layout.createSequentialGroup()
                            .addComponent(jComboBox1, 0, 173, Short.MAX_VALUE)
                            .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED)
                            .addComponent(jButton1, javax.swing.GroupLayout.PREFERRED_SIZE, 87, javax.swing.GroupLayout.PREFERRED_SIZE))
                        .addComponent(jScrollPane1))
                    .addContainerGap())
            );
            layout.setVerticalGroup(
                layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                .addGroup(layout.createSequentialGroup()
                    .addContainerGap()
                    .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE)
                        .addComponent(jComboBox1, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)
                        .addComponent(jButton1))
                    .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED)
                    .addComponent(jScrollPane1, javax.swing.GroupLayout.DEFAULT_SIZE, 189, Short.MAX_VALUE)
                    .addContainerGap())
            );
    
            pack();
        }// </editor-fold>
    
        private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) {
            DefaultComboBoxModel model = new DefaultComboBoxModel(getAvailableRoots());
            jComboBox1.setModel(model);
        }
    
        private void jComboBox1ActionPerformed(java.awt.event.ActionEvent evt) {
            File choosenRoot = (File) jComboBox1.getSelectedItem();
            if (choosenRoot != null) {
                FileTreeModel model = new FileTreeModel(choosenRoot, false, true);
                jTree1.setModel(model);
            }
        }
    
        public static void main(String args[]) {
    
            try {
    //            for (javax.swing.UIManager.LookAndFeelInfo info : javax.swing.UIManager.getInstalledLookAndFeels()) {
    //                if ("Nimbus".equals(info.getName())) {
    //                    javax.swing.UIManager.setLookAndFeel(info.getClassName());
    //                    break;
    //                }
    //            }
                javax.swing.UIManager.setLookAndFeel(javax.swing.UIManager.getSystemLookAndFeelClassName());
            } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | javax.swing.UnsupportedLookAndFeelException ex) {
                java.util.logging.Logger.getLogger(NewJFrame.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
            }
            //</editor-fold>
    
            /*
             * Create and display the form
             */
            java.awt.EventQueue.invokeLater(new Runnable() {
    
                public void run() {
                    new NewJFrame().setVisible(true);
                }
            });
        }
        
        private Vector<File> getAvailableRoots() {
            Vector<File> v = new Vector<File>(10, 1);
            File userHome = new File(System.getProperty("user.home"));
            if (userHome.isDirectory()) {
                v.addElement(userHome);
            }
            File[] roots = File.listRoots();
            for (File root : roots) {
                v.addElement(root);
            }
            String os = System.getProperty("os.name").toLowerCase();
            boolean isUnix = (os.indexOf("nix") >= 0 || os.indexOf("nux") >= 0);
            if (isUnix) {
                roots = new File("/media").listFiles();
                for (File root : roots) {
                    v.addElement(root);
                }
            }
            return v;
        }
        
        // Variables declaration - do not modify
        private javax.swing.JButton jButton1;
        private javax.swing.JComboBox jComboBox1;
        private javax.swing.JScrollPane jScrollPane1;
        private javax.swing.JTree jTree1;
        // End of variables declaration
    }

