How to get all the checked boxes of several trees in a same window?

What I am dealing with :

I am working on a window with several Checkboxes Trees (Java Swing) and I used samples of codes that I found in stackoverflow to make a JTree with JCheckBox objects. So I made a class CheckBoxNode, a class CheckBoxNodeRenderer and a class CheckBoxNodeEditor. Nevertheless, I don't understand what really happens when I check a box in a tree. I used a very simple "println" to see what happens in many functions like getTreeCellRendererComponent of the class CheckBoxNodeRenderer for instance.

What I would like to do :

I have three trees and I would like to get all the checked elements of each tree in a separate element, an array or an ArrayList. So then, I can work with the selected elements with just reading these arrays or ArrayLists. Of course, if I uncheck a box, the element must be removed from the array.

What I already tried :

I have to admit that I didn't have many ideas. I tried to understand exactly what happens when I check a box, with logs in many functions and I could observe that when I check an element in a tree, my logs are written more than three times (for instance a log in getTreeCellRenderer).

My code :

class CheckBoxNode extends DefaultMutableTreeNode {

    /**
     * 
     */
    private static final long serialVersionUID = 1155080395876568819L;
    private String _title;
    private boolean _selectedStatus;

    public CheckBoxNode(String name, boolean isSelected) {
        this._title = name;
        this._selectedStatus = isSelected;
    }

    //GETTERS

    public String getTitle() {
        return this._title;
    }

    public boolean isSelected() {
        return this._selectedStatus;
    }

    //SETTERS

    public void setTitle(String newTitle) {
        this._title = newTitle;
    }

    public void setSelected(boolean isSelected) {
        this._selectedStatus = isSelected;
    }

    public String toString() {
        return _title;
    }
}

CheckBoxNodeEditor

class CheckBoxNodeEditor extends AbstractCellEditor implements TreeCellEditor {

    /**
     * 
     */
    private static final long serialVersionUID = 2616799535763664121L;
    private CheckBoxNodeRenderer renderer = new CheckBoxNodeRenderer();

    //CONSTRUCTOR 

    public CheckBoxNodeEditor() {}

    //METHODS

    public Object getCellEditorValue() {
        JCheckBox checkBox = renderer.getNodeRenderer();
        CheckBoxNode checkBoxNode = new CheckBoxNode(checkBox.getText(), checkBox.isSelected());
        return checkBoxNode;
    }

    public Component getTreeCellEditorComponent(JTree tree, Object value,
            boolean isSelected, boolean expanded, boolean leaf, int row) {
        Component editor = renderer.getTreeCellRendererComponent(tree, value,
                true, expanded, leaf, row, true);
        // editor always selected / focused
        ItemListener itemListener = new ItemListener() {
            public void itemStateChanged(ItemEvent itemEvent) {
                if (stopCellEditing()) {
                    fireEditingStopped();
                }
            }
        };

        if (editor instanceof JCheckBox) {
            ((JCheckBox) editor).addItemListener(itemListener);
        }
        return editor;
    }
}

CheckBoxNodeRenderer

class CheckBoxNodeRenderer implements TreeCellRenderer {

    private JCheckBox nodeRenderer = new JCheckBox();
    private Color selectionForeground, selectionBackground, textForeground, textBackground;

    //CONSTRUCTOR

    public CheckBoxNodeRenderer() {
        Font fontValue;
        fontValue = UIManager.getFont("Tree.font");
        if (fontValue != null) {
            nodeRenderer.setFont(fontValue);
        }
        Boolean booleanValue = (Boolean) UIManager.get("Tree.drawsFocusBorderAroundIcon");
        nodeRenderer.setFocusPainted((booleanValue != null)&& (booleanValue.booleanValue()));
        selectionForeground = UIManager.getColor("Tree.selectionForeground");
        selectionBackground = UIManager.getColor("Tree.selectionBackground");
        textForeground = UIManager.getColor("Tree.textForeground");
        textBackground = UIManager.getColor("Tree.textBackground");
    }

    //METHODS

    protected JCheckBox getNodeRenderer() {
        return nodeRenderer;
    }

    public Component getTreeCellRendererComponent(JTree tree, Object value,
            boolean selected, boolean expanded, boolean leaf, int row,
            boolean hasFocus) {
        Component returnValue;
        String stringValue = tree.convertValueToText(value, selected, expanded,
                leaf, row, false);
        nodeRenderer.setText(stringValue);
        nodeRenderer.setSelected(false);
        nodeRenderer.setEnabled(tree.isEnabled());
        if (selected) {
            nodeRenderer.setForeground(selectionForeground);
            nodeRenderer.setBackground(selectionBackground);
        } else {
            nodeRenderer.setForeground(textForeground);
            nodeRenderer.setBackground(textBackground);
        }
        if ((value != null) && (value instanceof DefaultMutableTreeNode)) {
            Object userObject = ((DefaultMutableTreeNode) value)
                    .getUserObject();
            if (userObject instanceof CheckBoxNode) {
                CheckBoxNode node = (CheckBoxNode) userObject;
                nodeRenderer.setText(node.getTitle());
                nodeRenderer.setSelected(node.isSelected());
            }
        }
        returnValue = nodeRenderer;
        return returnValue;
    }
}

Let me know if you need more information about my code and I'm very grateful to all of you.