Speakers Hans Muller (Hans Muller) and Scott Violet (Scott)

Moderator Edward Ort (MDR-edO)

This is a moderated forum.

MDR-edO Welcome to today's Java Live! chat on JFC Swing. Our guests are engineers Hans Muller and Scott Violet, key members of Sun's JFC Swing component team. They'll answer your Swing-related questions. So let's begin.

pforhan: What is a realistic memory target for Swing applications? 64MB? 128MB?

Hans Muller: Small to medium sized Swing applications will run acceptably on a 32 MByte machine. However, two or three such applications running at the same time will probably cause more paging than is acceptable. A 64M target is a safe bet for running up to a handful of small to medium sized applications; for running large applications like application builders, 128MB is better.

dberansky: I'm using HTMLEditorKit to create a basic text editor. The problem I'm having is this: when I create an empty JEditorPane and set it to text/html, there is a 20-25 pixel margin between the first line and the top edge of the field. Is there any way to get rid of it? I'd like the text to be as close to the top edge as possible. Thanks

Scott: dberansk: Our HTML support uses CSS to attach styles to the HTML elements. The default styles can be found in javax.Swing.text.html.default.css. You can either override these styles in your HTML document, or try and replace them by creating your own StyleSheet with your own modified default CSS rules. Take a look at the javadoc for HTMLDocument and StyleSheet for more information on doing this.

jpaiz: hans: I read "cardpanel - an alternative to cardlayout" and tried to compile the code. I got an error: Exception java.lang.ClassNotFoundException is never thrown in the body of the corresponding try statement (CardPanelDemo.java: "public class CardPanelDemo"). How can I remedy this error? Also, is this the best way to implement an applet in the GUI style of a "wizard" (similar to install programs on Windows)?

Hans Muller: jpaiz: If I remember correctly, the CardPanel demo uses reflection to load classes for the panels in the demo. I'm afraid I'm not looking at the source code now. However, if there's a line that contains Class.forName() in the code than a ClassNotFound exception will be thrown. Perhaps you've commented that out? As for building wizards; you might check the wizard infrastructure that's part of the "BeanBuilder" demo that's on the Swing Connection web site. It's part of the article about "XML Persistence."

Scott: Question: How to enable right to left text on Swing text components? Answer: Right to left editing can enabled by setting the component orientation. ComponentOrientation is a property on Component. In locales that are right to left this should automatically be set for you.

Sandip Chitale: The current implementation allows only one JToolBar in a panel with borderlayout. I think modern apps require multiple independant tool bars. Is Swing going to support multiple dockable/floatable toolbars like framework component?

Hans Muller: We don't plan to create a more elaborate toolbar framework for the next release of Java^TM 2 (1.4). However, if there was a great deal of interest in that we could look into it.

jtr: With the current layout managers, the layout of HTML is problematic. For instance, JLabel can't really tell when to wrap lines (and assumes everything is on one line). Once either the width or height is known, the label wraps correctly. So, the problem is the label must know either it's height or width to do the HTML layout, but the layout manager don't provide this. Is anyone looking into this?

Scott: jtr: We are currently not investigating any special layout managers to do this. What you may try is multiple layout passes. After the size has been set, the component may make itself invalid again, so that you should do another layout pass. Please fill out an RFE in the bug paragrade if you have other specificsyou would like addressed.

Jonah: I'm just getting used to Swing/MVC. I see the value of MVC in programming, but I don't see how Swing components help implement it. For example: Suppose I want to "view" a model that consists of a structure that represents the weather outside. A simple "model" would be something like a struct or class with a few data members: double temperature; double humidity; double visibility; Now suppose I want to create a view into this "model" whereby I simply display (in a TextField) these numbers. Well, if I use Swing, the only recourse is to store a TextField's data in a *Document* model! How unnatural! The model should stay as close to the nature of the data as possible, not turn everything into Documents. My only alternative is to make my "model" a subclass of Observable, and make a TextField that is an Observer, and add it as a listener. Then it seems that I'm not making use of any built-in Swing MVC, I'm basically implementing my own MVC. I could resort to making my own custom model and view, but why do I need to make my own customs models and views for data as simple as a double or int? Shoudn't this be part of Swing? Why aren't there basic models and views to display simple numbers so I can store my "model" data in a form that is more natural to the data it represents?

john: I've noticed that Swing uses ints for constants in the API. I've occasionally used an incorrect constant because of this. Wouldn't it be much better to use constants of a particular class type in the API?

Scott: There is a currently mix of using ints and specifics instances for enumerations, text uses instances in a number of places, while other classes uses ints. We would recommend you use actual instances, as this avoid problems you are encountering. Unfortunately it would require incompatable changes in Swing to move to using Objects everywhere, which is why we have no plans to go back through the API and change everything.

Hans Muller: It's true that the Swing models are tailored to suit the GUI components that use them. So it's often the case that a Swing model is really just an "adapter" or a view of an application specific object. In your case buiding a Document that mapped from three doubles to a some text is surely more trouble than it's worth. In a case like that the application is better off modifying the text model indirectly by setting the textfields "text" property. As for views of primitive types like integers and doubles; presently the only relevant model is BoundedRangeModel (JScrollBar, JSlider), which is for integers. Developers have often asked for a "spinner" component for displaying integers, which we plan to add in 1.4. Presently there aren't any plans to provide a model for floating point numbers.

paforhan: We have a large application. Swing consumes a big chunk of memory. Any tips on reducing GUI memory footprints?

Scott: The first thing to look at is if you are loading your entire app before the user can do anything. Often times the whole application is not used in a typical setting, and therefore dynamically loading pieces of the application dramaticaly changes the footprint required. Beyond that I would recommend using a heap analysis tool, such as hat, OptimizeIt or the like to see where your largest memory consumptions are. Often times it is not where you think it is. We have also spent time making sure that Swing doesn't load more than it is needed, which should also help for small apps that aren't using large portions of Swing.

BNNRC: I have had a large problem with memory leaks in Swing. I find that JPanels and JFrames and JInternalFrames are causing Memory Leaks. My application uses large quanties of such objects and I allocate large chunks of memory in subclasses of each of these objects. I find that my only recourse is to tell my users to buy 512 MB of RAM or even 1 GB of RAM and to restart often. These bugs are all reported on the bug parade, but have not yet been addressed in even JDK^TM 1.3 RC1 is there any hope for reasonable performance from the garbage collector and for Swing to correctly dispose of the memory for its own objects? I writing a large 3D medical image processing application, which will be distributed under the GPL.

Hans Muller: BNNRC: We are very concerned about memory leaks in Swing/AWT and I apologize if the bug you submitted hasn't been looked at yet. Please send the bugid over. I'd recommend using Optimizeit (or JProbe) to isloate the source of leaks. One problem that people occassionally run into with images is that an image hangs on the component argument you provide when the image is created. People often use a Frame or some other long lived component for this value which causes the image to stick around.

panlasigui: Hello, I have a question concerning the proper (optimized?) use of the JTextPane class on large documents. I use the doc.insertstring method to insert lines into the document and am experiencing LONG delays before anything is viewable in the scrollpane. By large document, I mean something larger than 1000 lines of text. The document content is just simple text and attribute assignments are only for color. -Thanks.

Scott: panlasigui: In 1.3 we will be introducing a new View implementation in the text package, called ZoneView. The currente View implementations require all the children Views to be created, as you can imagine for large documents this seems unnecessary as more than likely the user will never view the complete document. ZoneView allows you to defined zones of the View that will only be created when accessed for (they become visible) . I would recommend taking a look at this class in the 1.3 RC releases that are currently out there. For future releases (perhaps 1.4) we are exploring turning this on by default, which will mean the text components will comsume far less memory for large documents, and insertions should be slower.

blair: Whats the future of the layouts? I read somewhere that GridbagLayout would probably be replaced because it is too unwieldy?

Hans Muller: blair: The Java Look and Feel group has been building what they hope will be a replacement for GridBagLayout. The new layout manager uses a simpler set of constraints and it comes with a JavaBeans^TM "customizer" that can be used to configure the layout in a GUI builder that supports customizers. Or standalone. The future of this layout manager isn't certain, it may become part of 1.4 or it may be released as a freebie demo.

David P...: I have a Swing Application that has multiple plug in tools. I also have cut/copy/paste menu items. Is there a way that I can tell what component has focus? So that I can determine which tool (plug in piece)has focus? I looked at FocusManager, but that is only good for keyboard focus stuff. It will not handle the case that a component receives focus from a mouse click. Thanks... David

Scott: David P: Frame defines the method getFocusOwner, which you can use to determine what Component has focus in a Frame. javax.Swing.FocusManager can be better thought of as a manager to determine what component should next get focus. It does not manager who has current focus. For 1.4 AWT and Swing are drasticaly changing how focus will be handled. This is in response to the numerous bugs that have been filed against focus. There will be better API for determining who has focus, listening for focus changes, and all around clean-up in 1.4.

john: What is the focus of Swing in JDK^TM 1.4 going to be? (I'd like more support for Toolbars too, but more support for other things is more important to me)

Hans Muller: Our primary goals for 1.4 are smaller, faster, better (fewer bugs). We're also working on better integration with the Windows and Macintosh desktops, an update to the Java Look and Feel, support for Windows2000, and a few new components; notably formatted text fields and spinners.

calcaino: I'm looking for info on dynamically changing color on a JTable after a user has edited a cell. Do you have any suggestions?

Scott: calcaio: You can create your own TableCellRenderer that basis its background color off of anything you like, such as when a cell has been edited.

Eric De Broeck: I have a glassPane that intercepts all mouseEvents. Beneath the glassPane there are nested Containers( derived classes from JPanel). In the case of normal mouseEventHandling, events propagates starting from the deepest component down to the first JPanel with registered mouselisteners where it is consumed. When I intercept the mouseEvent and send it via dispatchEvent to the deepest JPanel (got from getDeepestComponentAt()), it does NOT propagate to the first ancestor with active mouselisteners. What am I doing wrong? Thanks in advance, Eric De Broeck Belgium

Hans Muller: Eric De Broeck: You're not doing anything wrong; the glass pane idea doesn't really support "observing" mouse events because there's no support for really redispatching events. This is a common request and I've been looking into a way to support it directly for 1.4. To redispatch events, as you noted, you need to be able to find the top most component under the mouse that has a matching listener. Presently the bits that indicate this are private to the AWT.

Phil Bradford: Q: To run HTML (including applets, etc.) I'm using HTMLEditorKit and parsing through to catch these tags, trying to process them, etc. Is there a better (easier) way I am not aware of?

Scott: Phil B: It is not clear to me if you are using the HTMLEditorKit to create an HTMLDocument and parsing that. If you are doing this, I would recommend you use the ParserDelegator (javax.Swing.text.html.parser.ParserDelegator) yourself. You simply pass in an instance of HTMLEditorKit.ParserCallback (I believe that is the correct name) that is notified as the HTML is parsed. This way you don't have the overhead of creating an HTMLDocument. If you are already doing this, then I would say yes, this is a good way to parse HTML using already existing tools. There will be an upcoming article (on the Swing connection) showing how you can use this parser to parse the Netscape bookmarks file and show it in a JTreeTable.

john: Have (Metal L&F) Swing components been evaluated (perferably by professional usability folks) to determine how usable their UI is? Because they are visually so different from win95 and Mac, I find most users get mildly confused when they first see them. There are bigger issues, like the details button in the JFileChooser doesn't work, but it almost looks enabled in the UI (why is it there at all?).

Scott: john: Yes, the metal look and feel has been usability tested in the past. I believe with the file chooser we have just not had the time to add the details support. We are working on it for a future release.

Rama: I have an signed applet which brings up a JFilechooser on a button action. Sometimes the dialog takes more than a minute to show up, especially when there are disconnected network drives. Any tips on how to make it faster?

BNNRC: Is there going to be a better HTML parser integrated into Swing soon. One that would have support for cascading style sheets for example.

Scott: BNNRC: Swing has had support for CSS (level 1) for some time now. The class StyleSheet supports parsing of a CSS document. The HTML support allows you to attach CSS in the usual ways, either in the head of a document, as a link, or as a style attribute. If you are using the html support in Swing, I would strongly urge you to try out the 1.3 RCs, as the support has improved tremedounsly since early releases. That isn't to say it is complete in 1.3, just much better than previous versions.

Hans Muller: Rama--although you may not be able to speed up the file chooser, you can prevent the application from hanging while the file chooser is busily blocking on calls (!) by constructing the file chooser in a low priority worker thread. Check out the second threads article on the Swing Connection web site, Swing Connection.

Sandip Chitale: The inactive internal frame makes the glasspane visible to capture mouse clicks so that if the user clicks then the internal frame can be made active. The glasspane is then hidden. This prevents a clean use of glasspane by the user. The AWT frames do not use similar strategy (such as use of glass pane). Why can't the same technique be used for internal frames? The inactive internal frame could monitor the FOCUS_GAINED events using the Toolkit.addAWTEVentListener(FOCUS_EVENT_MASK); Check if the source is a descendent of it and make itself active? This will not require the glasspane based implementation. Apperantly the glasspane interferes with Drag and Drop functionality also.

Hans Muller: Sandip Chitale: tracking focus-in events isn't a reliable way to activate internal frames--they don't all have descendants that request focus on mouse pressed. The AWT doesn't implement activation at all. This work is done by the underlying window system which can use tricks like passive mouse grabs, that we don't have access to in Swing. We have changed the way this works a little for 1.3, check out the "changes in 1.3" article on Swing Connection.

Scott Mccullough: I am creating an application that presents similar to the Windows NT explorer and similar displays. A split pane with a tree on the left and when a node is selected, its children on the right. Usually there are four views to choose from. Small icons, large icons, list and detail. I have detail working as a JTable. I cannot figure out how to show the other three formats. I believe they are all similar and figuring out one will guide me through the rest. I've tried a JPanel with JTextFields, JLabels and JButtons. Each have problems. Any ideas? Any samples?

Scott: Scott Mc: You will probably want to use a JList with a custom ListCellRenderer. JList currently does not support more than one column though (newspaper type layout) as you will often see in the Windows Explorer. You could either add this support yourself, or wait until 1.4, which is when we plan on adding support for multi-columns in JList. Another problem will be editing, JList currently does not support editing, although again this should not be that hard to add yourself.

Dan Pritchard: How can I programmatically select a row in a JTable? JTable.setSelectedRow(int) does not exist?

Scott: Dan P: JTable uses a ListSelectionModel to maintain which rows are selected. You can get a handle to the ListSelectionModel it maintains and then invoke setSelectedRow on it. I believe JTable also has a method called changeSelection, which is a cover for this, you may want to investigate this as well.

MDR-edO We're down to the last ten minutes of the chat. However, because of the volume of questions in the queue, we'll go overtime--at least until 5 after the hour.

Richard Stack: I find I am often using JTable to display data that should be in objects, but I have to return it from the DB as a Vector of Vectors because this is the way it's optimized in AbstractTableModel. Is there any way to use a Vector of MyObject (Customer for example) with getters and setters and have it work with AbstractTableModel. Regards richard

Hans Muller: Richard Stack: you definitely don't want to copy the DB data into an TableModel unless there's no way to index it by row,col. What you really want to do is build a subclass of AbstractTableModel that has a reference to your vector of MyObject objects and maps column indices to MyObject properties.

Sandip Chitale: Can Swing support a JMenu factory, which has all the menu items to switch to all possible Look and Feels? The action handler for the menu items could travers all the JFrames in Frame.getFrames() array and switch their look and feels to selected look and feel. Alternatively there may be an explicit registeration step to register the JFrames whose l and f should be changed (similar to ToolTipManager.registerComponent strategy).

Hans Muller: Sandip Chitale: The truth is that we talked about providing a utility class that did this for quite some time however we've never quite found the time to do a good one. The code in the SwingSet2 demo is a pretty good example of this.

Kin Wong: Are there any techniques to improve scrolling in a JTable with a large number of rows?

Scott: Kin W: With 1.2.2 we added a client property on JViewport that when set enabled a different strategy for scrolling that is often times faster, and consumes less memory. This strategy is the default in 1.3. If you are using 1.2.2, take a look at the javadoc for JViewport to determine how to enable it.

john: I'm thinking of entering a RFE to place an event /first/ on the AWT event queue. This would help resizing of components from a ComponentListener among other things (if the ComponentEvent isn't first on the event queue you get the UI components doing a dance as one updates, then the next). Any plans to add this? (BTW: I think Swing is a great architecture, it is usually very easy/fun to use!)

Simon: Hi, my question relates to cursor problems I have with JDK^TM 118 and Swing111. When I am reacting to an event that will take time to finish, I cannot set the cursor inside this event handler, because the GUI is frozen (the AWT thread is executing my code so how can it change/repaint a different cursor on a Swing component), isn't it? What can be a workaround for this behavior if it not a bug nor my mistake? Almost all complex Java applications I've seen does not show the hourglass when doing long works (for example, Forté for Java, even if I appreciate it very much :-)

Hans Muller: Simon: this is one of the most often reported AWT bugs, and I apologize for the pain and suffering. It is fixed in 1.3 release (and in 1.2.2 I believe). BTW--If you're doing something time consuming on the event dispatching thread, you should really be using a worker thread, you don't want to hang the application. Take a look at the 2nd threads article on Swing Connection.

Scott: john: What you are hinting at is adding ordering to the beans event notification. This has been discussed numerous times though, and there are currently no plans to do it though. If you have a proposal for this, we would love to read about it.

Larry Lace: What versions of Netscape and IE support Swing for JDK 1.2 and upcoming 1.3? Area there and special requirements.?

glen_s: When will long term persistence of serialized objects be implemented?

Scott: Larry L: I do not have a definitive answer as to which versions, I believe we support NS 4.0 and newer, and IE 4.0 and newer. These are supported through the use of the plugin, which you can get more information about from java.sun.com/products/plugin. Each release of the JRE includes a new version of the plugin.

MDR-edO Well our time (and overtime) has ended. I want to thank all of today's partricipants for some excellent questions, and especially our guests Hans and Scott for their fine answers.

Hans Muller: glen_s: We've been working on this problem for some time; last year at JavaOne^SM we presented the status of a project to provide long term persistence for JavaBeans in general - including Swing components. This project has been going very well, it's now part of the "Java Community Process." You can find out more on the Swing Connection web site--there's an article about the project there and a prototype implementation. You'll find our JSR (Java Specification request) on Java.sun.com/JCP under the link for "JSRs accepted for development".

Scott: Thank you for your questions. For those of you that have unaswered questions, I would recommend you send them to Swing-feedback@eng.sun.com. Other resources you can use include the Swing Connection. Sorry for any other resources I forgot to mention.

MDR-edO Last moderator (me) signing off. The forum is now unmoderated

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