Mac OS Eclipse: preventing GUI tree memory
Since Mac OS Eclipse migrated from Carbon to Cocoa, the tree graphical widgets have changed their behavior. Previously, if you had a subtree that was deeply expanded, if you closed and re-opened its root, only its children would be visible, collapsed. With Cocoa, all of its descendants appear in the same fashion as before. This makes it difficult to clean up deep expansions.
Fortunately, there is a way to get the old behavior back, via a key combination: Right and left arrows without any modifier key open and close a folder. If you hold the option key, the right arrow expands everything (=be careful with that in the Eclipse Package Explorer) and the left arrow collapses everything. The next time you open a node you have open-left-closed, only its children are visible.