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Java Coffee Break

Reader Email Q&A

Dateline: 3/12/00

I recently returned from the Internet World Singapore conference. After being completely offline for about a week, I came back to what seemed like a ton of email messages, many looking for help. While I try to answer all my email in one way or another, that isn't always possible, especially when you have about 700 messages in your queue. I thought I would share with everyone some of the recent questions and answers. For technical support, it is best to post to the bulletin board area, that way the whole community has the chance to help and learn from the situation. With that said, here are six of the questions:

1. Does the recent security patch from Microsoft solve the security problems in their browser mentioned in the past feature?
   Not completely. It removes the existence check vulnerability [getSystemResource()] but still permits reading anything in the CLASSPATH from a class loaded over the network [getSystemResourceAsStream()]. [As an FYI, I've noticed that the site that had the problem applet up has been down lately.]

2. How do I generate a .java file from a .class file?
   I've added resources to the security resource list for this. Jad and SourceAgain may help. (Jad is free.)

3. How do I drag and drop nodes of a JTree within itself?
   I'll look into creating an article on this one. I've been asked this frequently.

4. What are short circuit operators?
   The || and && operators in Java will stop evaluating operands as soon as it is able to determine the final result. For instance, with the || operator, if the first operand is evaluated to true, there is no need to evaluate the second as the final result will always be true. If you really need both operands to be evaluated, use the | or & operators.

5. How do I display tool tip text specific to a node in a JTree?
   In a past article, I mentioned how to do this for a JList. For a JTree, it is basically the same thing. Subclass JTree and override getToolTipText() (and don't forget to register your component with the ToolTipManager).

6. In a past article, I mentioned you can use the Acme GifEncoder to save an Image to a GIF file, instead of using the Java 2 JPEGImageEncoder. How do you use it?

   Image image = ...;
   FileOutputStream out = 
     new FileOutputStream("test.gif");
   GifEncoder encoder = 
     new GifEncoder(image, out);
     

Other Tidbits

I'll be back next week with more things to do and places to go. If you have any comments about this week's feature, be sure to post them to the bulletin board. If you have any questions or topic suggestions, let me know or submit feedback. For technical questions, try to post them to the bulletin board area, instead of emailing me directly. That way, everyone can benefit from an answer, as well as offer answers. See you next time.

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