Question

I have a simple TreeCellRenderer which extracts a JButton from the node, and outputs it to the JTree.

public class ButtonCellRenderer extends JButton implements TreeCellRenderer {

  @Override
  public Component getTreeCellRendererComponent(JTree tree, Object value, boolean     selected, boolean expanded, boolean leaf, int row, boolean hasFocus) {
    //setBackgroundNonSelectionColor(tree.getBackground());
    ProgressButton b = null;
    if ((value != null) && (value instanceof DefaultMutableTreeNode)) {
      Object userObject = ((DefaultMutableTreeNode) value).getUserObject();
      if (userObject instanceof ProgressButton) {
        b = (ProgressButton) userObject;
        return b;
      }
    }
    if (b == null) {
      System.out.println("Null!");
      DefaultTreeCellRenderer defaultRenderer = new DefaultTreeCellRenderer();
      return defaultRenderer.getTreeCellRendererComponent(tree,
              value, selected, expanded, leaf, row, hasFocus);
    } else {
      System.out.println("Returning label");
      return new JLabel(b.getToolTipText(), b.getIcon(), SwingConstants.CENTER);
    }
  }
}

I’m not sure why, but it seems to be stuck looping, and eats about 30~50% CPU. Is there any way to eliminate this? Or not have to use a renderer to output a JButton into a tree?

I’ve added the revised code above, but now I’m getting a problem where the buttons don’t display properly (they all come out small).

Answer 1

You are calling super.getTreeCellRendererComponent without storing the value. If later on no renderer is created you call this method again (if c==null...). This is expensive for itself.

More important:

A renderer should be a component that is reused and only configured for the specific value to be shown. This is why the default implementation reuses a label and just sets the text, colors, border… That is why renderer calls are quite cheap.

You create a new JLabel every time you show a value: returnLab = new JLabel(text);. This is expensive. This method will be called for each and every cell shown on each repaint event. This is much more expensive than building a grid of components and defies the whole purpose of the renderer concept.

Please have a look into the default renderer implementation to see how to do it correctly. And have a look into the tutorial.