I do know servlets and JSP (or at the very least am studying them now). I am reading the EXCELLENT text "Core Servlets and Java Server Pages" by Marty Hall.
Just wondering what other topics I should be reading
Dan

Hi everyone,
I am going to be starting to work on my first big web project in a few months, and was wondering what I should be reading in the meantime. I don't know anything about web security or UML. Should I start learning about one of these? Which do you think is more important? Can anyone recommend some good books?
Thanks in advance,
Dan

Okay, Thanks for the reply folks!
Dan

Hi everyone,
I am very new to the wonderful world of setting up webservers; in fact I know only the basics about client-server architecture, and I think if I am hardpressed I might be able to SPELL "Servur" (er ... never mind). So to boldly go forth and grapple with my server-ignorance I am going to try and develop a web application using servlets. I am reading an excellent book on the matter "Core Servlets and JavaServer Pages" and so far it looks like a snap. However I think that 90% of my time and brain haemorrhages will come from just setting up the server, rather than writing actual code.
I think I will use the Apache Tomcat, but I have a few questions:
1) Apache is the webserver and Tomcat runs the Servlets and Jsp in that environment. Is this correct?
2) I have heard that setting up Tomcat is ... er ... *cough* ... CHALLENGING, so I was thinking of buying the book "Apache Jakarta-Tomcat" by James Goodwill. Has anyone bought this book, and if so can they recommend it?
3) If my assumption about (1) is correct, I will need to install the Apache Webserver first. Is this as challenging as setting up Tomcat, and if so will I need another book just to do that?
4) What are the system requirements for running Apache and Tomcat in a windows environment?
Any insights or advice would be very much appreciated
Dan

Okay ... this has always confused me.
Other than costing me many precious hours of my life, is there actually a REASON why Java is case sensitive? Or to be more general why on earth would we want any languages or O/S to BE case sensitive?
Dan

Hi everyone,
I am going to be writing a program that spawns a single thread to do the basic processing of the program, while the event dispatch thread listens to user events. As the loop that the basic processing is performed in is not trivial, is the only way to exit gracefully from this thread to poll some variable that is affected by user events? This would mean that in order to keep the GUI responsive I would have to keep repolling the variable after any time consuming processes within the loop. This seems kind of crude doesn't it?
i.e.
While(Variable says keep going)
{
Poll Variable
Stuff
...
Stuff
...
Poll Variable
...
Stuff
...
Poll Variable
etc
}

Is there a more elegant solution?
Dan

Hello everyone,
I have made a GUI program that is called from native code. Basically the GUI runs as a screensaver. When the GUI is single-threaded (i.e. the GUI Thread only) the program runs flawlessly. However when I make it multi-threaded after a while the screensaver stops running and when I hit alt-ctrl-del I see that I have one or more Java tasks running in the background. So obviously something is wrong with my threading. I am having a heck of a time tracking the progress of the Java code since when the code is called from the native code, there is NO command prompt window and hence I can�t do the standard: System.out.println(�Executing X_Routine�), trick for debugging. I tried using a text file log, but if the program crashes before it closes the log, then I don�t get any debugging info. So I guess my two main questions are the following -
1) What is the best way to track down errors in such a situation.
2) I really, REALLY miss having output automatically directed to the command prompt window. Is there anyway that I can force this?
Thanks in advance
Dan

Hello everyone,
I don't know anything about C or C++, but of course the project I am working on requires a java class to be called from an executable. The GOOD news is I found the C code that will do this in the book I am using (Core Java volume 2). The BAD news is I can't get the &**&^(*ing code to compile! Actually I can get it to compile, I just can't get it to link properly. The name of the code is InvocationTest.c.
I am using the free Borland compiler (V5.51) under windows 98. The book says that in order to compile the code under the Windows C++ compiler, I need to type:
cl -Ic:\jdk1.3\include -Ic:\jdk1.3\include\win32 InvocationTest.c c:\jdk1.3\lib\jvm.lib
In borland I assumed that the syntax would be
bcc32 -Ic:\jdk1.3\include -Ic:\jdk1.3\include\win32 -Lc:\jdk1.3\lib\jvm.lib InvocationTest.c
However when I do this I get :Error Unresolved external 'JNI_CreateJavaVM' referenced from C:\MyC++Source\InvocationTest.obj
I guess my questions are
1) What the heck does this MEAN?
2) How do I get it to play nice and compile?
Any hints or answers would be really, REALLY appreciated
Dan
PS - I AM using Java 1.3
PPS - I double checked and the jvm.lib DOES exist under c:\jdk1.3\lib

Sorry for the length of the post. I guess I should also say that the Java Tasks appear only when it is launched from the native code, not when I run the classes from the command prompt. I guess that means its definitely a problem with the native code.
Dan

Hello all you Java Wizards!
I found a very interesting site, http://kevinkelley.mystarband.net/java/sava.html, which allows you to write screen savers in java on Windows platforms. It uses compiled native code to invoke the java virtual machine, consults the control.ini to determine which class to load and run using that virtual machine. I was overjoyed since this is exactly what I was looking for, for a project I am working on. I tried it out, choose the native code as a screensaver within the control panel -> display, and it indeed worked! However I noticed that though it worked about 75% of the time, it would cease working after a while. Hitting-alt-ctrl-delete I saw that there were several instances of Java tasks running. I consulted the java code for the classes and saw that it was using the now deprecated stop() method. So I wrote my own classes to be called by the compiled native code. And this worked too! Except again it only worked 75% of the time and would cease to work after a bit. Hitting-alt-ctrl-delete again there were several instances of Java tasks running. Consequently I think one of two things are occurring:
1) Despite the fact that there are only two threads running in my java code (a main thread and a worker thread) somehow there is a deadlock, hence the java tasks that continue to run and somehow inhibit further java program starts by the native method. I�m not sure how this would be possible, but it is consistent with the �usually works, but sometimes doesn�t� property of my java code. However there is no Hanging of the GUI or anything that is run.
2) The problem lies not in the java code but with the compiled native code and somehow in the invocation API the DestroyJava function is failing to execute. This would explain why there is no Hanging of the GUI, but only Java tasks that fail to terminate. However I don�t know why the Java tasks would only fail to terminate sometimes.
I really, REALLY hope it is the first possibility (but I think it is number 2). I don�t know any C++ or C, and I really don�t want to spend 6 months learning it just to write some native code that will run a JVM as if it were a screen saver.
I tried to contact Mr Kevin Kelley, but the email on the site is no longer working. Does anyone have any ideas as to what I should do here? I have included my java code in the hopes that the flaw lies within it. I have not included the native code, since I only have the compiled native code ... unfortunately.
My Java classes are quite simple. A small window with a panel is created. There is a JTextField in the Panel, and a custom event source (Counter) starts looping in a for loop, and each loop number is passed to the JtextField so that the Panel begins counting up. A MouseMove over the Panel informs the Counting thread to cease, dispose methods are called and the thread exits. Here are the classes
----------------------------------------------
import java.awt.*;
import java.awt.event.*;
import java.io.*;
import java.util.*;
import javax.swing.*;
import javax.swing.event.*;

public class DanScreen
{
public static void main(String args[])
{

Frame frame=new Frame("Dan's Mad Project");
frame.setSize(200,200);
SaverWindow dan=new SaverWindow(frame);
dan.show();
frame.show();
}
}
---------------------------------------------------
import java.awt.*;
import java.awt.event.*;
import java.io.*;
import java.util.*;
import javax.swing.*;
import javax.swing.event.*;
public class SaverWindow extends Window implements Runnable
{
private Frame frame;
private Counter c;
private int count=0;
private CountPanel panel;

public SaverWindow(Frame aframe)
{

super(aframe);
frame=aframe;
setLocation(0,0);
setSize(300,300);

panel=new CountPanel();
c=new Counter();
CountListener tListen=new CountListener();
c.addTimerListener(tListen);
panel.add(c);
ScreenMouseListener sml=new ScreenMouseListener();

panel.addMouseMotionListener(sml);
add(panel);

c.startNow();

}

public void panelCleanUp()
{
dispose();
frame.dispose();
System.exit(1);
}

public void run()
{
panel.setCount(""+count);
}
class CountListener implements TimerListener
{
public void countIncrement(TimerEvent te)
{
count=te.getCount();
EventQueue.invokeLater(SaverWindow.this);
}
}
class ScreenMouseListener extends MouseMotionAdapter
{
public void mouseMoved(MouseEvent me)
{
System.out.println("MouseMotion event");
c.stopCount();
panelCleanUp();
}
}
}
---------------------------------------------------
import java.awt.*;
import java.awt.event.*;

import java.util.*;
import javax.swing.*;
import java.io.*;
public class CountPanel extends JPanel
{
JTextField countField;


public CountPanel()
{
countField=new JTextField(20);
add(countField);

}
public void setCount(String s)
{
countField.setText(s);
}
}
--------------------------------------------------------
import java.awt.*;
import java.awt.event.*;
import java.io.*;
import java.util.*;
import javax.swing.*;
import javax.swing.event.*;
public class Counter extends JComponent implements Runnable
{
private int count=0;
private EventListenerList listenerList;
private boolean stopRequested=false;
private Thread t;
public Counter()
{
listenerList=new EventListenerList();
count=0;
t=new Thread(this);
}
public void startNow()
{
t.start();
}
public int getCount()
{
return count;
}
public synchronized void run()
{
for(;;count++)
{
try
{
Thread.sleep(5);
}
catch (InterruptedException e)
{
}
EventQueue queue=Toolkit.getDefaultToolkit().getSystemEventQueue();
TimerEvent event=new TimerEvent(this);
queue.postEvent(event);
if(stopRequested)
break;
}
}
public void stopCount()
{
stopRequested=true;
}
public void addTimerListener(TimerListener listener)
{
listenerList.add(TimerListener.class, listener);
}
public void removeTimerListener(TimerListener listener)
{
listenerList.remove(TimerListener.class, listener);
}
public void processEvent(AWTEvent event)
{
if (event instanceof TimerEvent)
{
EventListener[] listeners=listenerList.getListeners(TimerListener.class);
for(int i=0;i<listeners.length;i++)>
{
((TimerListener)listeners[i]).countIncrement((TimerEvent)event);
}
}
else super.processEvent(event);
}

}

Well there it is. I would really welcome any suggestions that the good people on this site might have, I really have no idea how to proceed here.
Dan

Hi Everyone!
Ye Gods! Look at the number of posts in here!! (First time here)
I told my friend that I would be happy to do some Java Server work for him so I can get some marketable experience. The only problem is ... I DON�T KNOW ANYTHING ABOUT SERVLETS OR JSP!!! Its a pretty straightforward project though, he wants a program on the server that takes in info and stores it into a database, so I am assuming I�m going to need to know about servlets and JSP (and maybe a bit of JDBC). Can anyone recommend any good books on the subject? I am a SCJP so I am comfortable with the Java syntax, but know next to nothing about running Java on a Server. Ideally I would like something that starts with the basics and builds from there with LOTS of examples to illustrate what they are talking about. Maybe even something that builds an example Server project???
Also, my intuition tells me that the best way to design this is to have the program collect the info into an XML file, and then from the XML file put it into the DB. I�m not sure why my intuition tells me this ... something about being able to easily change the DB later. But I don�t understand how this could be, after all the server is still going to have to translate the XML into the DB, so where is the value in going to XML first? Of course it is possible that my intuition is totally off base here, its usually only super accurate when it comes to blind dates!
Thanks in advance,
Dan

Okay! I had some juice and thought about it. I got it, I got it. I thought EventListenerList was in the package javax.swing, but in reality I have to import javax.swing.event. Doh! Sorry for the short curcuit there ... it was one of those days, you know?
Dan

Okay, I must be blind, or my Java compiler is whacked. Why in the name of the heavens won't this stupid code COMPILE??? I have been doing all kinds of swing stuff in this directory, and now all of a sudden this happens:
import javax.swing.*;
public class Frustrated extends JComponent implements Runnable
{
// Copied DIRECTLY from java api docs!!!
EventListenerList listenerList = new EventListenerList();
}
The compiler keeps complaining:
C:\classes\Frustrated.java:20: cannot resolve symbol
symbol : class EventListenerList
location: package swing
javax.swing.EventListenerList listenerList = new javax.swing.EventListenerList();
WHAT DO YOU MEAN YOU CAN'T RESOLVE THE CLASS EVENTLISTENERLIST ??? ITS A STANDARD JAVA CLASS!!!
GRRRRRRRRRRRRRRR!
Well, I feel a little better now ... but I think I need a new keyboard. Anyway, I would be grateful to anyone that can point out my stupidity in this case ...
Dan

That does help quite a bit. I have a chapter in a book that shows how to make custom events so I'll work from that. One question though. In my original code I can understand why the countup would not occur at a constant rate (since it would depend on when the thread for painting was executed) but why would there be periods of a second or so when there was nothing in the text field? Is it because during those times the entire GUI is being cleared and then painted?
Actually on second thought, I lied, I don't understand why the countup is not at a constant rate. I'm not doing anything to the GUI so why is it painting it over and over again? (assuming that I am correct that this is the cause for the jerky count rate)
Also I just wanted to say that the Certification Study Guide you co-wrote was a damn fine piece of work. I doubt I would have scored as high on the SCJP exam if I didn't have that book.
Dan

Hi everyone,
I am experimenting with GUIs and am trying to do something relatively simple. I have a countdown program (hence the NASA reference) that displays numbers in a textfield. Well, technically it counts UP, but that is beside the point. Anyway, I have a separate thread to do the counting, and it seems to work, excpet that periodically the numbers in the textfield flash off for a second, but the counting still continues, and then the numbers reappear. I am suspecting that this has something to do with Java repainting the GUI. Anyway, here is the code, its pretty basic:
import java.awt.*;
import java.awt.event.*;
import java.io.*;
import java.util.*;
import javax.swing.*;
public class Supercount
{
public static void main(String args[])
{
Frame frame=new Frame("Dan's Mad Project");
frame.setSize(200,200);
Window dan=new Window(frame);
dan.setLocation(0,0);
dan.setSize(300,300);
CountPanel panel=new CountPanel();
dan.add(panel);
dan.show();
frame.show();
Thread runner=new Thread(panel);
runner.start();
}
}
public class CountPanel extends JPanel implements Runnable
{
JTextField countField;
public CountPanel()
{
countField=new JTextField(20);
add(countField);
}
public void run()
{
int count;
for(count=0;count<10000;count++)
{
countField.setText(""+count);
repaint();// My attempt to fix the problem
}
}

}
Anyone have any ideas on how I can get a nice smooth counting display? I suppose slowing down the counting would work, but are there any other ways?
Thanks in advance,
Dan

Hi there everyone,
I'm a beginner when it comes to DOM and XML.
I downloaded the DOM Parser from Sun for java and have been examining the methods for the various classes. It seems that they make Element a subclass of Node. Now why would they make such a distinction? Aren't all nodes in a document tree elements and vice versa?
Thanks in advance
Dan

Hello Everyone,
I have this really cool idea (I think) for a screensaver program. Of course I can't write it in Java since the screensaver is run by the operating system. I really want to keep the platform independence (and avoid writing native code in C++ (shudder) ). So what I want to know is, is there anyway that I can make a java program ACT like a screensaver. Specifically when it is run it sits in the background listening to keystrokes or mouse activity (even within another program) . If after a certain time there isn't any such activity then it does something until that activity occurs.
I don't think there is anyway to listen for ALL such activity (since in java one adds these listeners to a specific component) since I would need the Java program to figure out that there is no such activity going on even in any other programs. But I thought I would see if anyone has any workarounds ...
Dan

Hello everyone,
I am new to the developer forum. I passed by SJP last week with good marks, and now I am trying to figure out what to do next (I miss the hours slamming my head against the wall in study!).
So I think the next thing I am going to tackle is the Developer's exam. I am a hand's on kind of guy when it comes to development so thought this would be the best. Is it realistic for someone with only a bit of Java experience to pass this exam if they are willing to do the grunt work required?
Also, since you have to submit your code for inspection, I would imagine there is a tidy industry of qualified "Proofers" that would examine your code (for a fee) and point out weaknesses, design flaws etc. Am I right in assuming this? Where would one find such people?
Thanks in advance
Dan

Hey everyone!
I passed the Programmer Certification last week with 86% and now I am trying to figure out what to work on next. I have had no Java knowledge until I started studying 3 months ago. What kind of certification is realistically attainable within another 3-4 months of study? Architect? or Developer? Which is more coveted? And which one has more free/purchases resources?
One head hunter tells me that knoweledge of J2EE is definitly an asset, but I'm not sure which exam that is pointing me to.
Please keep in line that any code that I will be writing will have to be done on my single computer (windows 98) at home. I have no network with which to experiment.
Thanks in advance
Dan

Lets see ... its kind of a blur. I got a few on input/output constructors. Lots and LOTS on overriding and overloading, a couple on using synchronized code and basic thread concepts, one on bit shifting, one on the Object Wrapper Classes, a few on basic String concepts (such as that they are immutable) and String Buffer concepts. Lots and Lots on initializations and array concepts, Layout Managers. Some on abstract classes, inheritance and interfaces. The last thing that I remember is I got a few on primitive casting.
Surprisingly I didn't get ANY on casting objects. And I don't remember any questions on components ... but I wouldn't read too much into that. It was probably the luck of the draw.
Hope this helps

Okay I think I understand. Its not that the InterruptedException kills the thread, but rather within catch InterruptedException, this is where the programmer should write code to ensure that that thread dies. Is this correct?
Dan

Hello fellow ranchers. Well I did it! Last Sat I passed with 86%. I can safely say I couldn't have done it without this cool website and JQ+ (Worth every penny). I know of about 6 questions I would have got wrong if not for that marvellous piece of software.
I would also like to take this time to everyone that helped me with my numerous "BUT WHY???" questions, in particular Jim Yingst and Cindy GLass.
Dan

I was hoping someone could clear something up for me. I am still not entirely sure what the interrupt method of Thread DOES. I have read that it should be used to replace the deprecated stop() method. So that makes it seem like the interrupt kills another thread. But then I also have read that a Sleeping Thread that recieves an interrupt() call moves immediately into the Ready state; when it gets to run it will execute its InterruptedException handler. So this makes it seem like it actually awakes the thread rather than kills it. What am I missing here? What happens to the thread after it handles the InterruptedException? Does it continue to execute?
Thanks in advance
Dan

Wow! I had no idea that abstract classes could have constructors. Thanks so much for the info
Dan

Thanks everyone ... I think I understand now. Abstract methods are meant to be overridden and you can't override a static method (since it is shadowed like member fields).
BTW Michael that book you co-wrote was the best money I ever spent!
Dan

Is there a reason why static methods cannot be abstract, or is it just a brute fact?
Thanks in Advance,
Dan

Okay, here is a straightforward question:
If abstract classes have no constructors (since one cannot have instances of them) how is it possible to extend from them? If I make a subclass isn't there always an implicit call to super() in that subclasse's constructor? But in this case there is no super constructor ...
Thanks in advance
Dan

Okay ... I guess this was a fundamental misunderstanding on my part. So except for accessing final local variables, an inner class defined inside a static context is very similar to a static inner class. Correct?
Dan

But this is exactly my point. The anonymous class since it is defined in a static method has no enclosing instance related to it. Thus it cannot refer to any enclosing instance fields. But all inner classes except for static inner classes must have such an enclosing instance. But the above code with the anonymous class seems to violate this rule.
Dan

But I don't understand the difference. I thought local method classes also needed an instance of the outer class, otherwise how could they have access to outer member fields?
Dan

I get it ... thanks for the info!
Dan

Ah yes ... I forgot that high order bit. Thanks for the reply
Dan

Does anyone know why this code works?
abstract class AbClass { public abstract void m(); }
public class OuterClass
{
public static AbClass getClass()
{
return new AbClass()
{
public void m() { }
};
}
}
An anonymous class is being created in the static method getClass(), but it is being created witout any instance of the Outer class? I thought this was never allowed ...
Dan

I have been using the JQ+ tester which has been worth every penny. However I have come across a question which seems wrong. But since they have been always right before, its probably me that's wrong. here is the question:
If write(0xAABBCCDD) is called on an instance of FileOutputStream, what will be written to the destination of the stream?
They say the answer is -
The byte 0xDD
But this seems wrong: Here is my reasoning, A Byte can only have a max value of 127 and DD is 221 in hex. In binary this is 11011101. Only the low order bits would be retained for a byte which is 1011101 which is 93, or 5D in hex. What am I missing?
Dan

That is what I suspected was going on (i.e. the instances are converted to instances of the respective abstract classes). But what classes (i.e. the subclasses) are being instantiated when the getGraphics() and getInputStream() are used?
Thanks in advance
Dan

I wrote this post, but it seems to have vanished, so i'll try again. Here is a brain teaser that I hope someon can solve. You cannot have instances of an abstract class. And yet InputStream and Graphics are both abstract classes. Once can get instances of these classes using the getInputStream() and getGraphics() methods respectively. So what gives?
Thanks in advance
Dan

I have read from one source that Java uses UTF 8 to internally represent variables and such. But another source claims that it uses Unicode. What is the real story?
Thanks in advance
Dan

Ah ... right! What a stupid question on my part.
Thanks
Dan

Hey there Java Land,
A while back someone started a thread on "Worst Interviews", and it had some great stories. I thought it might be
fun to revive that thread, and also include "Worst Job Experiences" as well. I'll start -
My worst interview was at this really big company and you went into a bunch of rooms for a battery of questions
from various people. So I went into this one room and a particularly cold individual was there and started firing the
usual questions "Give an example of a stressful situation and how you dealt with it", "What is your weakest skill?"
etc . So I initiated my part of the ritual and started firing back my prepared responses. Except ... well ... his
questions kept repeating others that he had just asked, other than a slight rewording. Thus he would ask "What is
your weakest skill?" ... and then a few minutes later "What skill do you need to improve more?" etc. So I just
stared at him perplexed and asked "How does that question differ from the weakest skill question?". He just
scratched his head, looked embarrassed and glanced at his list. He said "I don't know ... but I have to ask these
questions". Sounds like a tight little bureaucracy to me ...
Dan

Does anyone know when a String literal that exists in the string pool is garbage collected, if ever?
Thanks
Dan