To support editing of the tree column we can not make the tree editable. The reason this doesn't work is that you can not use the same component for editing and rendering. The table may have the need to paint cells, while a cell is being edited. If the same component were used for the rendering and editing the component would be moved around, and the contents would change. When editing, this is undesirable, the contents of the text field must stay the same, including the caret blinking, and selections persisting. For this reason the editing is done via a TableCellEditor.

Another interesting thing to be aware of is how tree positions its render and editor. The render/editor is responsible for drawing the icon indicating the type of node (leaf, branch...). The tree is responsible for drawing any other indicators, perhaps an additional +/- sign, or lines connecting the various nodes. So, the renderer is positioned based on depth. On the other hand, table always makes its editor fill the contents of the cell. To get the allusion that the table cell editor is part of the tree, we don't want the table cell editor to fill the cell bounds. We want it to be placed in the same manner as tree places it editor, and have table message the tree to paint any decorations the tree wants. Then, we would only have to worry about the editing part. The approach taken here is to determine where tree would place the editor, and to override the reshape method in the JTextField component to nudge the textfield to the location tree would place it. Since JTreeTable will paint the tree behind the editor everything should just work. So, that is what we are doing here. Determining of the icon position will only work if the TreeCellRenderer is an instance of DefaultTreeCellRenderer. If you need custom TreeCellRenderers, that don't descend from DefaultTreeCellRenderer, and you want to support editing in JTreeTable, you will have to do something similar.