See NetBeans issue 51826
(http://www.netbeans.org/issues/show_bug.cgi?id=51826)

Tree UI incorrectly refuses to expand nodes for the first time when using right arrow key.
In NetBeans we use a special tree model over file abstractions that is filled on demand. Our nodes correctly report they are not leaves, but they initially have no children (children count = 0). If you ask them for their children for the first time, they start processing and may report no children initially, but will fire an event once the children are fully computed.
This scheme worked correctly on previous JDKs, but has problem with right arrow expansion on JDK6.0 (b25)
On JDK1.6 the BasicTreeUI checks the number of children in advance and stops processing in case of zero. It works second time because the node is already internally populated.

###@###.### 2005-03-01 14:04:11 GMT