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Easy Learn Java: Programming Articles, Examples and Tips - Page 158


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Java Newsletters: Java Newsletters Archive: 168

Go to all tips in Java Newsletters

=== [ The Java FAQ Daily Tips, weekly publication ] ===

Issue No: 168 1 July 2003
13435 subscribers

Foreword: Excuse me for possible mistakes. English is not native language for me.

In this issue:
  • 1. Why does not exist "JavaNotFoundException"?
  • 2. I am sure that in my program I create 100 new threads and when I use isAlive method it shows often less than 100 threads... I have not killed even one of them!
  • 3. When I use Java to write my program under some specific OS,...
  • 4. Latest posts on our message board
  • 5. Link to Java FAQ

  • Hello dear friends!

    Tip 1

    Question: Why does not exist "JavaNotFoundException"?
    When I deliver my Java program to customers often Java is not installed on theirs machines. Having such exception I could in better form (GUI popup, for example) inform my customers about the problem...

    Answer: Is not it obvious that to be able to find the absence of Java with Java program you need Java Smile

    Java wimps please close your ears ... For the Java programmer who
    thought he knew everything there was to know about Java, have a
    look at the most advanced Java newsletter archived on the website
    http://www.smotricz.com/kabutz Guess what, it won't even cost you
    anything! Subscribe today - you won't be disappointed.


    Tip 2

    Question: I am sure that in my program I create 100 new threads and when I use isAlive method it shows often less than 100 threads... I have not killed even one of them!

    Answer: Good, short and clear explanation I found in Java tutorial on SUN's site:
    "The API for the Thread class includes a method called isAlive. The isAlive method returns true if the thread has been started and not stopped. If the isAlive method returns false, you know that the thread either is a New Thread or is Dead. If the isAlive method returns true, you know that the thread is either Runnable or Not Runnable. You cannot differentiate between a New Thread or a Dead thread. Nor can you differentiate between a Runnable thread and a Not Runnable thread."

    --
    John.


    Tip 3

    Question: When I use Java to write my program under some specific OS, I always set some environment variables to control the application program. For example, CLASSPATH.
    What is about other variables that I should be aware of? And how can I set them?

    Answer: Java defines own environment which is different from the default one provided by the underlying OS.

    You can define your own "environment" by using

    java -Dname1=myvalue1 -Dname2=myvalue2


    Latest posts on our message board
    bloking Java plugin in applet tog

    How can the default call of the java plugin on the applet tag be blocked so an applet can be run without the plugin. I have an applet that runs fine with out the plugin but stalls with it.
    help here


    Almost no hair left! NullPointerException in EventDispatchThread.

    I get this error after app has been running a while.
    What is the problem and where can I fix? It doesn't happen on my dev machine, but only on the production system.
    Help will be much appreciated!
    Quigrim

    java.lang.NullPointerException
    at javax.swing.plaf.basic.BasicProgressBarUI.getGenericBox(BasicProgressBarUI.java:477)
    continues here


    Java Web Start

    I have a problem with An Application that is launched by
    web-start.

    I would like to load class-files from jar's or zip-files that are
    not part of the spec. in the Applications jnlp-file.

    I can download the jar from a web-server and place the jar's/zip's in a catalog. And then try to instance the classes that i want from the jars/zips.
    I have tried to write my own class-loader. And it works ok if
    i run the application locally ( not from web-start ).
    continues here


    Watch Training Video on Enterprise JavaBeans For Free(DSL version)

    Hi all,
    We just posted new Training Video on Enterprise JavaBeans(DSL version),it may be helpful for you all.
    Thanks

    Direct Url:
    continues here


    Help in JTextPane

    Hi,

    I am displaying a html file in JTextPane, When I do changes in that file, click on send, These changes should be sent to other user which highlighted text which is changed, I know the highlighting part, but how to send only the changes which have been made, I don't know. I have implemented DocumentListener but I don't know why it is not responding when I attach a HTMLEditor kit with JTextPane
    help here


    JPanel on top of another JPanel

    I've got two JPanels. And I want to show one on top of the other:

    http://www.wflyers.nl/java.gif

    The red one has to be on top of the big bleu JPanel.
    I've tried JLayeredPane() already, but that failed.
    Does anyone has got an idea how to fix this problem.
    help here


    Updating randomAccessFile

    Hi again, ne wday new problem.
    I have a GUI that takes the attributes for a student, name, address etc and stores it to a random file. I everything works fine, but now I have to be able to update the information in the file. When I veiw the student information in the studentpanel, I should be able to edit the textfields and click on an update button that will update the file. I don`t want to append on to the existing file, I just want to overwrite it with the new information...at least thats what I think it should be doing.
    I created my update button and Now I am in the process of figuring out the actionevent for it,,,,except I do not have a clue, I havn`t even been able to find any basic examples of this.
    This is what I have so far.
     

    code:

    if (e.getSource() == jbtUpdate)
    continues here


    1 comment | Printer Friendly Page  Send to a Friend | Java Newsletters | Score: 0
    Posted by jalex on Monday, February 02, 2004 (15:58:39) (2884 reads)

    Java Newsletters: Java Newsletters Archive: 167

    Go to all tips in Java Newsletters

     === [ The Java FAQ Daily Tips, weekly publication ] ===

     Issue No: 167                                            5 June 2003
    13103 subscribers    

    Foreword: Excuse me for possible mistakes. English is not native language for me.

    In this issue:
  • 1. I know that Hashmap implementation is not synchronized. How can I synchronize it?
  • 2. Could you tell me what is advantage of Spinner over Combo box?
  • 3. Latest posts on our message board
  • 4. Link to Java FAQ

  • Hello dear friends!

    Tip 1

    Question: I know that Hashmap implementation is not synchronized. How can I synchronize it?

    Answer: Really good answer often can be found in API!
    "If multiple threads access this map concurrently, and at least one of the threads modifies the map structurally, it must be synchronized externally. (A structural modification is any operation that adds or deletes one or more mappings; merely changing the value associated with a key that an instance already contains is not a structural modification.) This is typically accomplished by synchronizing on some object that naturally encapsulates the map. If no such object exists, the map should be "wrapped" using the Collections.synchronizedMap method. This is best done at creation time, to prevent accidental unsynchronized access to the map:

    Map m = Collections.synchronizedMap(new HashMap(...));

    The iterators returned by all of this class's "collection view methods" are fail-fast: if the map is structurally modified at any time after the iterator is created, in any way except through the iterator's own remove or add methods, the iterator will throw a ConcurrentModificationException. Thus, in the face of concurrent modification, the iterator fails quickly and cleanly, rather than risking arbitrary, non-deterministic behavior at an undetermined time in the future.

    Note that the fail-fast behavior of an iterator cannot be guaranteed as it is, generally speaking, impossible to make any hard guarantees in the presence of unsynchronized concurrent modification. Fail-fast iterators throw ConcurrentModificationException on a best-effort basis. Therefore, it would be wrong to write a program that depended on this exception for its correctness: the fail-fast behavior of iterators should be used only to detect bugs."

    From Java API (v 1.4.1)

    --
    John  


    Tip 2

    Question: Could you tell me what is advantage of Spinner over Combo box?

    Answer: Really no advantages, excluding one: spinners are sometimes preferred because they don't require a drop down list that can obscure important data. Indeed, in Spinner component you can "spin" thousands of values (for example year). Let's now imagine drop down window which contains all years of human history Smile


    Latest posts on our message board

     

    Threads

    I have developed this little program that illustrates the problem that is similar to a different one I am making. I wonder how you make the first method run through completely then go onto paint(g) which runs through the second. As of now, all three: down,first, and second appear simultaneously.

    // The "Threads" class.
    import java.applet.*;
    import java.awt.*;

    public class Threads extends Applet
    continues here


    Class question

    Hi,
    My question is simple:

    I have a Frame (Frame1) with a textfield component on it and a jbutton and
    another Frame (Frame2). When i push a jbutton on Frame1, Frame2 appears. All
    well so long. The problem is here: I have another textfield (editable) on
    Frame2 and a jbutton. I want to get the text of textfield on Frame2 when i
    push the button and have the text BACK ON FRAME 1.

    I have a .java file for each Frame: Frame1.java and Frame2.java. I 'm
    creating an object like this on Frame2.java:
    Frame1 obj=new Frame1();
    and i get Frame1's methods with obj.
    All seem good, i'm getting no error message, but it doesn't work.

    As you may have understood i'm a little bit rookie so any help would be appreciatable. I' m working on Borland JBuilder 8

    Thanks on advance.
    continues here


    GUI - refresh ..it will not end

    Hi there

    Since a very long time I'm stuck in the same problem again & again...

    Situation:
    I'm using swings JFrame where I add an instance of a Class that extends JLabel. I've overridden the paintComponent(Graphics g)-method where I do the whole draw-stuff and finally call super.paintComponent(g).

    Problem: The content of the frame does not refresh, until the window is resized etc.

    Code:

    private JFrame myFrame = new JFrame();
    continues here


    MS-Java emulation on Java 2?

    Hi,

    There is an old avatar chat applet (example: http://eagles.chatserve.com/ip.html) called InstantPalace. The applet works great, but it's pretty old, and only runs on the MS-Java and older "Java 1" JREs. So users who have upgraded to Java 2 JREs can't use it. The Applet was created by a company that is no longer in business, so chances of it ever being updated for Java 2 compatibility are, unfortunately, not very good.

    I was wondering if there was a way to emulate MS-Java inside of a Java 2 applet, so older Java2-incompatible applets such as this one could be used on systems with Java 2.
    continues here


    centering applet on screen

    Hi,
    I have an applet that I want to position in the top center of my screen,
    When I run the applet in the applet viewer it shows up in the top left corner of my screen, Dose anyone have any ideas on how I can fix this, this is the html code I am using. I also tried using a center method in this code, but then my applet didn`t appear on the screen. Any help wopuld be greatly appreciated.
     



    4 comments | Printer Friendly Page  Send to a Friend | Java Newsletters | Score: 0
    Posted by jalex on Monday, February 02, 2004 (15:57:18) (2911 reads)

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