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JTree representing a graph

I am using the JTree Swing utility to represent a Tree that actually have loops. I have a single node called root, but some of the children will eventually point back to other parts of the tree, thus not making it a true tree, but rather a graph.
My Java application keeps locking up, (no exceptions being thrown, no stack overflow... etc) when I try to use the little gray arrows to expand and contract parts of the graph.
My question is, does JTree require that none of the DefaulMutableTreeNodes not contain a loop?
If so, how do we represent something like that using a JTree utility. For example, when you are debugging an application say in eclipse, and you can infinitely use the variable tree in debug mode to keep on looking through a looped object. That is the behavior I am looking for.
Any suggestions?

I don't think it's a problem that nodes in a Jtree loop on themselves. Apparently you have a problem only with an "expand all" button, which makes sense because an expand all method will go recursively through the nodes until they have no sons.
Jtree does not have an expand all button by default, so I'm guessing yours is already customized...? My suggestion would be either remove the button, or customize the code to stop the expansion if findind a node that was already expanded higher in the hierarchy.

Horizontally flipping a JTree

I want to visualize a set of linked objects by focusing on one element and showing all referenced objects and descendants in a tree to the right. That's business as usual.
But if i want to show the referencing objects (i.e. the objects pointing at my selected element) to the left of my selection i'd like to add a little twist. I want it to be a "reverse tree" - a tree with the structure nodes and lines on the right side.
That way the selected element (as root node) would be in the middle of the two trees and at least in theory it would be less confusing to the user.
Is there a way to flip the tree structure (not the text of course) horizontally in a JTree?

I'm pretty confident that there isn't an easy solution.
Probably the best you can do is, dig into the paint/repaint method of the tree until you find the place where the actual drawing is happening. Then create a tree with your own implementation of that.
Beware that you have to do the same thing for any kind of event handling, in order to find the correct node that was clicked on.

maybe you have look at JTreeTable,

It seems like you have to implement the TreeCellRenderer interface and make your own realization of getTreeCellRendererComponent and paint methods.
Excuse me for short answer and maybe wrong even. It just a small hint.

Programmatically Scroll an SWT Table horizontally

Similar question, but not exactly the same.
table.showColumn() is helpful, but the scrolling only has the granularity of the column width. But I want a more precise control of the scroll location.
Consider the following use case. I have two tables that I know are of the same width and have the same column widths. And I want to implement some kind of a scroll synchronizer so that when the user scrolls one table (horizontally), the other table scrolls to the same location.
EDIT:
On the Eclipse forum there seems to be the same question and some working ideas, but no resolution.
EDIT:
I discovered this behavior on Windows

The method setOrigin(x,y) in ScrolledComposite should help:
Scrolls the content so that the specified point in the content is in the top left corner. If no content has been set, nothing will occur. Negative values will be ignored. Values greater than the maximum scroll distance will result in scrolling to the end of the scrollbar.

I'm afraid I can't get a satisfying result in Windows Vista/7 either, but felt I was getting close.
I believe you will have to grab the Table's horizontal scroll bar by using table.getHorizontalBar(). Then, you can specify scrollbar.setSelection() to make it move to a specified position.
This is where I get stuck. Somehow, you have to notify either the Table or the ScrollBar that the value has changed. I've tried everything from update() to notifyListener(), but no dice. It seems that it is merely a matter of laying out, but layout() doesn't have any effect, either.
Incidentally, bear in mind that the ScrollBar's parent (type Scrollable) is not a ScrolledComposite like I had expected, but is actually the Table itself.
I hope this gives you some ideas and helps you find a solution. If so, please let me know, since it's bugging me now, too!

Having poked around in the ScrollBar source a bit, it looks like there are numerous (windows) bugs that have been overcome at one point or another. This may be another, though you didn't mention your OS, nor did Paul, so it's hard to tell.
All the "change the scroll bar position" functions end up calling SetScrollInfo which is package private. I suspect that the intention is for this to actually update things the way you want.
None of that solves your problem. Thankfully the same source also hints at a solution:
Slider.
You'd have to reimplement all the scrollbar behavior within slider, but once done, that should give you the control (har) you want. Hopefully. OTOH, you may run into exactly the same OS bug (if bug it be), and be back at square one.
At THAT point, you definitely register it as an Eclipse UI bug.
PS: Have you searched the Eclipse Bugzilla for anything similar? Poking around a bit turned up this bug related to the scroll bar being out of sync with a tree view in the Navigator (on PC Linux-Motif, but working fine in Windows). I suspect you'll find similar issues if you dig a bit more.

Java- updating JTree

I've got a JTree which I'm using to display some (unsurprisingly) hierarchical data. Part of the spec is that the user can change the data source (atm it's just between files). Now, when this happens, I can rebuild the data and the tree nodes with no problem. But, I'm having substantial difficulties getting the tree to update the changes. I tried removing it from it's scrollpane and replacing with a new JTree, but I didn't see any such. I've tried removing all from the JTree and didn't see any effect.
How can I make the JTree display changes after it's been constructed?
Ninjedit: Yes, I did call updateUI().
Another edit:
I also wanted to replace the tree's current data with my new data. However, I don't see any methods that will take the DefaultMutableTreeNode that I constructed with. Even if I just remove the JTree and call updateUI on it's containing ScrollPane, nothing happens. Or if I use repaint instead.

It could be that the proper events (the JTree internal events) are not being fired. For example, you can add nodes either by using node.add(...) or even better, model.insertNodeInto(...) (assuming you're using the DefaultTreeModel). In this case, the latter method is preferred as it will fire appropriate events that will cause the view (the JTree) to update correctly. It's possible that your problem isn't with redrawing the UI, but in fact notifying the view that the model has changed.
So, I would suggest looking in to how you're dynamically modifying your JTree, and if possible I'd suggest using the DefaultTreeModel as your model to drive the view.
And just to make sure, you've read through the Sun JTree tutorials, right?

Is there a way to have expander icons for multiple roots in a JTree?

I have a JTree with multiple "roots" (Of course, I actually have an invisible real root with multiple children).
The nodes expand and collapse on double click, but there's no visual indication that you can do this as there is no expander icon.
This is made worse by the fact that the tree is collapsed by default, but expanding the "roots" doesn't really help, as each has many children and it would look cluttered.
Is there a way to display the expander icons without making the real (and utterly valueless) root visible?
Any other suggestions to make the display clearer welcome.

Would tree.setShowsRootHandles(true) be a good way to display those "expander icons" ?
A tree typically also performs some look-and-feel-specific painting to indicate relationships between nodes. You can customize this painting in a limited way.
First, you can use tree.setRootVisible(true) to show the root node or tree.setRootVisible(false) to hide it.
Second, you can use tree.setShowsRootHandles(true) to request that a tree's top-level nodes — the root node (if it is visible) or its children (if not) — have handles that let them be expanded or collapsed.
Check also your look and feel to be sure what the renderer does with your tree.