Trees - The Definitive Guide to Java Swing - page 624

Figure 17-6. A JTree with no connection lines
The following lines produce horizontal lines between level-one nodes:
UIManager.put("Tree.line", Color.GREEN);
JTree tree = new JTree();
tree.putClientProperty("JTree.lineStyle", "Horizontal");
Figure 17-7 shows how the horizontal lines appear.
Figure 17-7. A JTree with horizontal level lines
TreeCellRenderer Interface
Each of the nodes within the JTree has an installed cell renderer . It's the responsibility of the
renderer to draw the node and clearly display its state. The default renderer is basically a
JLabel , which allows you to have both text and an icon within the node. However, any compo-
nent can serve as the node renderer. The default renderer displays an icon that represents the
state of the node.
■ Note The tree cell renderer is just that—a renderer. If the renderer were, say, a JButton , it wouldn't be
selectable but would nevertheless be drawn to look just like a JButton .
The configuration of each node renderer is defined by the TreeCellRenderer interface. Any
class implementing this interface can serve as a renderer for your JTree .
public interface TreeCellRenderer {
public Component getTreeCellRendererComponent(JTree tree, Object value,
boolean selected, boolean expanded, boolean leaf, int row, boolean hasFocus);
}