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Tag Archives: Swing

Enabling tooltips on a JTree

12-Aug-08

Thinks i keep forgetting. Today: Enabling a JTree in J2SE to show different tooltips on his nodes:

1. Create a custom tree renderer like so:

import java.awt.Component;
 
import javax.swing.JTree;
import javax.swing.tree.DefaultMutableTreeNode;
import javax.swing.tree.DefaultTreeCellRenderer;
 
public class TooltipTreeRenderer  extends DefaultTreeCellRenderer  {	
  @Override
  public Component getTreeCellRendererComponent(JTree tree, Object value, boolean sel, boolean expanded, boolean leaf, int row, boolean hasFocus) {
    final Component rc = super.getTreeCellRendererComponent(tree, value, sel, expanded, leaf, row, hasFocus);		
    String tooltip = "Compute some arbitrary text depending on the node (which is hidden behind 'value')";
    this.setToolTipText(tooltip);
    return rc;
  }
}

2. Set this renderer

aTree.setCellRenderer(new TooltipTreeRenderer());

3. Keep wondering, why the tooltip doesn’t show…

4. Register the tree with the ToolTipManager (which isn’t necessary for nearly all other Swing Components…)

javax.swing.ToolTipManager.ToolTipManager.sharedInstance().registerComponent(aTree);

5. Enjoy :)

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On Java Threads: A fairytale of a tutorial

12-Jul-07

I always thought that the Java Thread API is something… strange. If you work in a frontend application, things like running long-running tasks in the back without having the GUI ugly frozen and not responding should be somewhat simpler.

SwingWorker has been around for quite a time but made it just recently into the core API (Java6). Furthermore i don’t think that it’s the right thing for performing enduring tasks like checking for mail and pushing a result with a second thread into a database, for example.

Don’t get me wrong, i use SwingWorker quite often, but it didn’t fit my needs and furthermore, i wanted to learn more about Java Threads.

My goal / task was a little daemon that regularly checks an email account and a samba share for some files, load them into an Oracle Database and executes a longer running db procedure. The checking should be suspendable and stoppable independently, the configuration should be reloadable.

I throw some interfaces and abstract classes at the vm and boom, it was that simple ;)

Things i’ve learned:

  • Always start the GUI in it’s own thread, never use the main thread. Sure, most programs will work fine, but it can get confusing. Use SwingUtilities to do so.
  • A thread once terminated is not reusable. Never ever. So don’t interrupt them if you plan on resume them later.
  • Know the primitives, i.e. build in locks (synchronized and wait())
  • Know the task scheduling frameworks (Executors and ExecutorServices)
  • Read the tutorials here, here and maybe here

The following demo can start 7 producers and one consumer, both are synchronized via a BlockingQueue (i actually used a SynchronousQueue at work, as the files must only be removed if they were taken by the db). Both the producers and consumers can be suspended, resumed and stopped. I never ever will start a thread by hand again if not necessary. The threads are managed by an ExecutorService.

For the tasked mentioned above this thing works fine. If anyone comes up with a better idea, let me know.

I had fun to write it, maybe you have fun to read. Be aware, the program is not a good example of organizing classes, i put everything in one file just for the sake of being a demo.

But apart from that, the demo could serve as an example of what came to Java with Java 5 and 6 as i use a lot of generics, enums and enhanced for loops, in case you haven’t seen this.

To compile and run the stuff you need at least a Java5 JDK (get it here, download this file JThreadDemo.zip, unzip it and type

javac snow/white/JThreadDemo.java
java snow.white.JThreadDemo

If you read this, i’ll guess you’re familiar with the JDK, java packages and the whole crap.

Get the whole fun after the click:

More…

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