| Re:Correct use of exceptions |
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Index ‹ java-programmer
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- 2
- Reset button cannot clear fields after displaying error messagesHello
my form extends from ValidatorForm
and making use of validator.xml and validator-rules.xml,
The reset button can clear fields within form
if the submit is not pressed.
If I pressed the submit button and
error messages display on the top of the form.
And then now I click the reset button again,
fields cannot be cleared.
Why is it so?
- 3
- Ant Javadoc failure when building help.I'm getting this error when trying to compile javadoc in ant from my
buildxml:
Any ideas?
C:\umg\java\web\dbtest\WEB-INF\src\build.xml:64: Javadoc failed:
java.io.IOException: CreateProcess: javadoc.exe -d
C:\umg\java\web\dbtest\WEB-INF\doc\api -classpath
C:\umg\java\web\lib\servlet-api.jar;C:\umg\java\web\lib\struts.jar;C:\umg\ja
va\lib\umg-db.jar -sourcepath
C:\umg\java\web\dbtest\WEB-INF\src -version -author
java.com.umusic.ecrm.web.test error=2
what's error=2????
this is in my build.xml:
<!-- Build Javadoc documentation -->
<target name="javadoc"
description="Generate JavaDoc API docs">
<delete dir="./doc"/>
<mkdir dir="./doc"/>
<javadoc sourcepath="./src"
destdir="./doc/api"
packagenames="*"
author="true"
private="true"
useexternalfile="yes"
version="true"
windowtitle="${project.title} API Documentation"
doctitle="<h1>${project.title} Documentation (Version
${project.version})</h1>"
bottom="Copyright © 2003">
<classpath refid="compile.classpath"/>
</javadoc>
</target>
- 3
- Infinite loops in hashCode() and equals()What do you think the following fragment prints?:
List l = new ArrayList();
l.add(l);
System.out.println(l.hashCode());
Trick question. The result is an infinite recursion (i.e. a stack
overflow), since the hash code for a List is calculated from the hash codes
of its members.
Likewise, the following causes an infinite recursion, since lists are
defined to be equal when they have the same members.
List l1 = new ArrayList();
List l2 = new ArrayList();
l1.add(l2);
l2.add(l1);
System.out.println(l1.equals(l2));
These cases are simple to spot, but the same situation could occur with any
cyclic graph of objects that compute hash code and/or equality based on the
values of their members. Also, equals() and hashCode() are often called
implicitly, for instance when adding an object to a HashSet or HashMap.
I don't see any way this could be addressed other than by keeping track of
which objects have already been processed by the current hashCode() or
equals() call, and there's no way to do that without changing the method
signatures, to, say, add a Set:
in Object:
public final int hashCode() {
return hashCode(new HashSet());
}
public final int hashCode(Set processed)
{
if (processed.contains(this)) {
return System.identityHashCode(this);
}
else {
processed.add(this);
return this.calculateHashCode(processed);
}
}
public int calculateHashCode(processed) {
return return System.identityHashCode(this);
}
with calculateHashCode(Set) being the method that classes can override and
hashCode(Set) the method List et al. call on their members. And that is a
pipe dream, since it isn't possible to make this sort of incompatible change
at this late date.
- 4
- NoClassDefFound puzzleNoClassDefFound is my least favourite error message. This one has me
stumped. I have been very sick the last few days and my brain in not
yet fully engaged, so I hope it is something simple.
I compile this fine, but when I run it, it says class
com.mindprod.example.TestProgessFilter is not defined.
The program seems too simple to have a NoClassDefFound problem.
package com.mindprod.example;
import java.io.BufferedReader;
import java.io.File;
import java.io.FileInputStream;
import java.io.FilterInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
/**
* @author Roedy Green, Canadian Mind Products
* @version 1.0, 2007-08-03 Created with IntelliJ IDEA.
*/
public class TestProgessFilter extends FilterInputStream {
/**
* tracks how many bytes we have read so far
*/
long progress;
// -------------------------- PUBLIC INSTANCE METHODS
--------------------------
/**
* Constructor
*
* @param in input stream to progress monitor
*/
public TestProgessFilter( InputStream in )
{
super( in );
}
/**
* Reads the next byte of data from this input stream.
*/
public int read() throws IOException
{
int ret = super.read();
progress++;
reportProgress();
return ret;
}
/**
* Reads up to byte.length bytes of data from this input stream
into an
* array of bytes.
*/
public int read( byte[] b ) throws IOException
{
int ret = super.read( b );
progress += b.length;
reportProgress();
return ret;
}
/**
* Reads up to len bytes of data from this input stream into an
array of
* bytes.
*/
public int read( byte[] b, int off, int len ) throws IOException
{
int ret = super.read( b, off, len );
progress += len;
reportProgress();
return ret;
}
/**
* Skips over and discards n bytes of data from this input stream.
*
*/
public long skip( long n ) throws IOException
{
long ret = super.skip( n );
progress += n;
reportProgress();
return ret;
}
// -------------------------- OTHER METHODS
--------------------------
/**
* report the progress to the user
*/
private void reportProgress()
{
// this is a dummy routine. A real version would send an event
// to a progress meter.
System.out.println( progress );
}
// --------------------------- main() method
---------------------------
/**
* test driver
*
* @param args arg[0] is UTF-8 filename to read
*/
public static void main( String args[] )
{
try
{
// O P E N
FileInputStream fis = new FileInputStream( new File( args[
0 ] ) );
TestProgessFilter tpfis = new TestProgessFilter( fis );
InputStreamReader eisr = new InputStreamReader( tpfis,
"UTF-8" );
BufferedReader br = new BufferedReader( eisr, 400/*
buffsize */ );
// R E A D
while ( true )
{
if ( br.readLine() == null )
{
// line == null means EOF
break;
}
}
// C L O S E
br.close();
}
catch ( Exception e )
{
System.err.println( e );
e.printStackTrace( System.err );
}
}
}
--
Roedy Green Canadian Mind Products
The Java Glossary
http://mindprod.com
- 4
- Java to C++ converterHi,
I am looking for Java to C++ converter tool. Any existing tool available?
Thanks for your help in advance.
- 4
- portal library needed ?Hi all ,
I am trying to build a portal which will consist of functions like log
in , user management and some cms stuff and will probably develop more in
the future. So I am trying to search for some portal building library. Has
anyone try one of these portal library like jetspeed, jPorta, liferay ... ?
Is it really that useful ? On what basis should I use one ? As i think the
learning curve maybe quite large that I am sure i can build faster without
it. But I am not sure if I would need it when I further develop the site.
And can anyone share some pros and cons of the library.
Thanks.
Perseus
- 5
- How to Escape a Single Quote in Java 1.5 javax.xml.xpath.* ?Hi everybody,
How to escape a single quote in java 1.5 javax.xml.xpath XPath queries?
Eg. meta[@name='Tom Jastrzebski's question']
I have tried numerous approaches that typically work but none of them did.
Does anybody KNOW how to do it?
Thanks in advance.
Tom
- 9
- package and jar filesHi,
I am new to Java. I hope someone can give me a hint.
What is the difference between package and jar files and do you use them ?
thanks
John
- 9
- ToolTip for Graphical ItemsHello,
I'm trying to make a tool tip pop up whenever the user does a
mouse-over on a filled rectangle that I've drawn on the screen. I have
no trouble creating the rectangle
Rectangle test = new Rectangle();
And it seems like there should be something like
test.setToolTipText("rectangle"), but as far as I can tell, there's
nothing like that. Is there some way to do this?
Thanks,
Ben
- 9
- UTF 16 (byte[]) <--> String?Hi,
is there a convenient way to convert unicode that's stored in byte array to
java String?
and vice-versa?
e.g. for a single single unicode,
the higher byte would be in byte[0],
lower byte[1]
and byte[2], byte[3] = 0. null terminated
the byte array of unicode is generated from a C program and transfered over
the network ..
looking over the String API doesn't reveal much ... or am I overlooking
something?
Thanks in advance.
- 9
- I write Tic-Tac-Toe in JavaThis is the most sophisticated game known to mankind and I'm not sure
if Java is good enough for it, but I'm trying anyway.
- 15
- R: JTable and db connectionThere is a good example in JTable example ad www.sun.com. By the way, it is
based on the idea of copying all the records in a Vector array, and then
send all to the JTable...
IMHO this isn't a good approach, but it is a good example to understand the
JTable
Bye
Giuseppe
Liguori Ferdinando <email***@***.com> wrote in message
bhl1va$55u$email***@***.com...
>
> Could you help me to definy a trouble.
> I wish see data retring db connection in a JTable.
> Could you mailing an example.
> Thanks.
>
>
- 15
- How to get current jar pathHi! I'm working on an application that should run on an usb pen using
an embedded Derby DB. I need the DB to be on the USB pendrive with the
application.
Pen filesystem should look like this:
/
- application/
- application.jar
- lib/
- embeddedDB
using "user.dir" system property i get the path from where the jar has
been launched, while I need the path where the jar is. How can I do?
- 15
- A strange linux command execution problem from ProcessHi All,
I am using Process class to run scripts on a Fedora Core Linux
bash shell
All of my scripts are running except tho one in which i am using diff
command.
I am using simple diff command. My script is
-------------------------------------------------------------------------------------
#/bin/sh
if [ $# -eq 0 ];
then
echo "Usage: newFile oldFile outputFile"
exit
fi
FILE1=$1
FILE2=$2
OUTPUT_FILE=$3
echo "diff -c $FILE1 $FILE2 > $OUTPUT_FILE"
#diff -c $FILE1 $FILE2 > $OUTPUT_FILE
diff -c $FILE1 $FILE2 > $OUTPUT_FILE
------------------------------------------------------------------------------------------------
And I am also consuming the error and output streams so not blocking
the process.
the process returns with exit value > 0.
It would be a great help to me. If you help me solve this problem.
-Thanks,
Ratnesh.
- 16
- Just a Great Big Scrollable LineHello,
I am a bit new to java and the java swing GUI.
I am writing a JApplet.
What I am trying to do is draw a line (say from (0, 0) to (1000, 1000)) and
have the applet supply automatic scrollbars so that the user can see the
whole line (sounds stupid - I know, but its a step in my direction).
Anyway, I tried to inherit from a JLabel, change the inherited comopnent's
paintComponent method to draw a line and put the inherited component in a
JScrollPane. However, this only resulted in a Line which was only partially
seen and no scrollbars. Moreover, I discovered that if I just add text to
my label with the setText method then I get auto scrollbars if I make the
applet smaller than the text size. This means that the setText method is
doing something that defines it's boundaries for the JScrollPane to react
to. So, my question is: How do I tell the JScrollPane that my inherited
JLabel is 1000x1000 (and not just the size of the text)?
Thanks,
Aviv.
|
| Author |
Message |
no name
|
 Posted: 2006-2-17 17:20:00 |
Top |
java-programmer, Re:Correct use of exceptions
When we talk about exception, it means that in some situation which we think
that it should works this way, but it isn't. For example, when we write
something to connect to remote SMTP server, we assume that the remote server
should be available but actually it is down... In this case, the exception
happened... So we need the exception handling to show our error message to
user and log the error.
Hope this helps!
Guoqi Zheng
http://www.big8reader.com
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Index ‹ java-programmer |
- Next
- 1
- struts form population from an object model...flangelli wrote:
<snip>
> I have a business object model with attributes throughout that are
> mapped to different form beans. Every time that a form bean (jsp) is
> returned to the user's browser, I need to have a place to access my
> object model to retrieve the data from and populate the bean before it
> is displayed. So far it seems that the only time an action class is
> given "command" is AFTER the form submission, I need control on a page
> by page basis to retrieve the values from the object model into the
> bean so the jsp can render the beans values.....anyone had a problem
> similar to this? Thanks in advance - Flangelli
There's nothing which "requires" you to forward to a JSP; you could
just as easily forward to an action. The hitch here is that the
ActionForm will be populated according to the request parameters if
you just perform a forward. The solution is simply to specify
redirect="true" in the forwarding action so that the request
parameters get lost.
Just be careful in your validate method when using this mechanism:
you're users will be irked if the first time they see a page it
contains all manner of error messages. Since you often provide a
reset button on a form, the smart way to approach the situation is
to hold off generating errors if all form fields are blank (or
have the default value).
If this doesn't make perfect sense then repost and I'll dig up
some sample code. Or contact me off-line.
- 2
- Forcing System.gc()I have an app that, at one point, really bogs down as so many objects are
created and released in a lengthy process.
I am wondering if I may not be able to improve performance by System.gc() in
some "right" places in my code (wherever those might be!). It seems to me
though, that the gc facilities in Java are so good, that this is something
best left up to the JVM, and NOT mess with putting System.gc() in anyplace?
I am on WinXP / Vista and JRE 1.6.x. TIA, R. Vince
- 3
- Mp3 converter to WavHi,
I just need to convert a mp3 file to the Wav format.
Is there any free package existing, or do i have to write my own program ?
In that case, do you know any link that could help me to understand how to
do this ?
Thanks !
- 4
- Jars built with JDK 1.3 and JDK 1.4 interoperatingThe Runtime Environment is JRE 1.4. The latest code I have written has
been compiled with JDK 1.4. However it depends on some packages written
and compiled with JDK 1.3. Is there anything to look out for in this
kind of setup or should I have to recompile the older code with 1.4? I
have tested the whole thing and it works, but I wanted some more
information. It is a swing code and I need the JProgressBar's
indeterminate state which is available only in JDK 1.4.
Any update is welcome. If there is any document explaining the above,
that would be perfect. I searched but I was not able to find any
reference.
Thanks
JS
- 5
- My bean doesn't APPEAR on my JSP page!Hi, All!
I have this simple bean (below), and i make the .class using JBuilder 7.0.
I tryed to insert this bean into my JSP page:
<%@ page contentType="text/html; charset=windows-1251" %>
<html>
<head>
<title>
Jsp1
</title>
</head>
<jsp:useBean id="bean0" scope="session" class="bean1.KivaHanTester" />
<jsp:setProperty name="bean0" property="*" />
<body>
<h1>
JBuilder Generated JSP
</h1>
</body>
</html>
BUT I CAN't see this bean, when i open my JSP (IExplorer + Apache).
May be i need to init this bean, like init() or show() i don't know.
Thanks.
SOURCE CODE:
package bean1;
import java.awt.*;
public class KivaHan extends Canvas {
private String msg;
private int width, height;
public KivaHan () {
this ("Coffee: 10 lira");
}
public KivaHan (String s) {
this (s, 200, 200);
}
public KivaHan (String s, int width, int height) {
msg = s;
this.width = width;
this.height = height;
setForeground (Color.cyan);
setFont (new Font ("Serif", Font.ITALIC, 24));
setSize (getPreferredSize());
}
public void paint (Graphics g) {
Dimension d = getSize();
FontMetrics fm = g.getFontMetrics();
int len = fm.stringWidth (msg);
int x = Math.max (((d.width - len) / 2), 0);
int y = d.height / 2;
g.drawString (msg, x, y);
}
public Dimension getPreferredSize () {
return new Dimension (width, height);
}
}
package bean1;
public class KivaHanTester extends java.applet.Applet {
public void init () {
add (new KivaHan());
}
}
- 6
- Java GSM encoding from micHi
I'm trying to encode a microphone stream into GSM using
org.tritonus.lowlevel.gsm.Encoder but I am receiving just static noise -
I've checked the raw PCM output and it's fine. Is there anything obvious
that's missing here?
Thanks
__________________________
The mic is opened as:
AudioInputStream ais=null;
DataLine.Info info_mic = new DataLine.Info(TargetDataLine.class,
new AudioFormat(AudioFormat.Encoding.PCM_SIGNED, 8000.0f, 16, 1, 2,
8000.0f, false)
);
TargetDataLine mic = (TargetDataLine) AudioSystem.getLine(info_mic);
mic.open();
mic.start();
ais = new AudioInputStream(mic);
_____________________
And the GSM frame encoder is:
/*------*/
byte [] gsmframe(AudioInputStream ais){
byte [] encd = new byte[33];
try{
byte [] b = new byte[320];
ais.read(b,0,b.length);
DataInputStream di = new DataInputStream(new ByteArrayInputStream(b));
short [] buf = new short[160];
short j=0;
for(int k=0; k<buf.length; k++){
j=di.readShort();
buf[k]=j;
}
org.tritonus.lowlevel.gsm.Encoder enc = new
org.tritonus.lowlevel.gsm.Encoder();
enc.encode(buf, encd);
}catch(Exception e){
System.out.println("error with microphone reading "+e);
return null;
}
return encd;
}
/*-------*/
- 7
- Struts and AA based on a database
Hello:)
I have a question concerning authentification/authorization and
elements visibility on a Web page in Struts. How to manage the
visibility of control elements in a Struts-based application? The
information about users should be stored in a database and not in XML
configuration files. How to use role based or/and function based
authorization system and how to retrieve the rights from a database and
store them in the Principal object? The application is mantained within
Tomcat application server. So, how to do this? Or, being more precise,
is there any open-source library which provides such a functionality or
should I develop everything from scratch? Do you have some examples for
such stuff?
best regards,
Ania
- 8
- jtreetabledear java professional,
i want to create a grid using jtreetable. i find the sample code in
the java.sun.com. but it is trickly to understand for me. do you
have any code
(simple code) for using the jtreetable ? i want to simple jtreetable
example program with sample data. do you have the code please send me
to my mail id
email***@***.com.
i also search in the net. but i only very less no. sample code related
to jtreetable. that code also so tricky. do you know any link that
contains simple
jtreetable program?
with regards,
balamurugan se
- 9
- extract numbers from picture?is this called pattern matching or AI in java? how can you extract a number
that is on a jpeg or bmp/gif/tiff ? is there any java package doing this?
thanks
- 10
- [Q] Saving imageI am looking for a solution to how to make a background image
permanent in a Java application.
My application can have a background image, but when it saves its
file, the background image is not included in the saved file. Is there
a convenient (or right) way to save a gif (or jpeg or png) image into
an application file?
Thanks in advance.
Young-Jin
- 11
- Communicating with a servlet using NIO?Is it possible for a client applet to communicate with a servlet using NIO?
I know it's possible using standard IO but I would like to implement a
servlet that accepts NIO connections from clients and interacts with them.
Is this possible? I don't want to use a special port because of firewall
considerations.
--
And loving it,
-Q
_________________________________________________
email***@***.com
(Replace the "SixFour" with numbers to email me)
- 12
- How do i do if-else condition in Struts ?How do i do if-else condition in Struts ?
logic:equal does not do it . how struts tag could be used in the JSP
page for an if-else condition ?
how to do it ?
Can anybody provide an example ?
- 13
- batch update as a single transactionHi,
I'm doing a JDBC batch update, writing several thousand rows to a single
table. As I understand it a batch update can partially succeed, so some of
my rows might get written and some not. I'd like the batch update to either
fully succeed or completely fail, commit or rollback in other words. Is that
easy to do? I'm pretty new at this.
Thanks,
John
- 14
- Eclipse vs NetBeans vs Jbuilder under LinuxHello everyone,
I've tried the above 3 IDEs in the last year and thought I might make some
comments and ask for your thoughts. Just for interest sake and please don't
start a Holy War ;-)
I originally used netBeans for development, but switched over to Jbuilder
because we where doing tomcat/struts development and my boss said it had
better support. I didn't really get to use netBeans struts stuff but it did
seem a bit weak in comparision.
I would have thought Borland would have a great editor, but I find it very
buggy in comparison to netBeans. Some of the things I have had problems
with include the cursor not being moved when you click in the text area
(this tends to screw up click and drag rearrangement of text or do it when
you don't mean too), auto-formatting of code rearranging it until it won't
compile, method parameter popups not always accessable, method parameter
popups not able to show the names of parameters - only the type, and some
others I can't remember right now.
However, the struts support in JBuilder does seem to be better than netBeans
and runs quite well. Over all the IDE also seems a little quicker and I
quite like the way that you can have multiple projects open and flip
between then with ease. netBeans doesn't seem to handle multiple projects
as smoothly as JBuilder.
I also tried Eclipse at home a couple of time in the last 6 months and at
the moment I can't see why many people are using it. On both occasions I
found also sorts of nasty bugs which tended to simple drive me nuts. The
last time time I used it for example, I found that it would not run the
code I had just edited. I.e. if I could load a project, made some changes
and hit the run button, it would run the code without the changes included.
In order to get the changes it, I had to explicitly do a save before each
run. This sounds trivial but can get very annoying, both netBeans and
JBuilder run the code you are editing, not the last saved code.
Eclipse also seemed to have a strange concept of projects. It looked rather
good with being able to see multiple project trees at the same time until
it came to running them. Then it appeared to separate the concept of
running a projects from the projects themselves and I had to effectively
re-setup again. I also found that if I had en error in one project, it
would fail the compile even if I was in another project. So whilst I could
have multiple projects open at a single time, it seemed to have trouble
understanding which projects I was in and what it was to compile. This
resulted in me having to unload/reload projects on a regular basis. I also
remember not being that happy with it's editor either, I can't remember
exactly why right now.
So, I would have to say that at the moment, I would tend to use netBeans for
general development, JBuilder for struts and Eclipse not at all.
--
cio
Derek
- 15
- Simple question for those who understand recursion well. Please help.I have a tree represented as a linked list of simple objects
(nodeId/parentId pairs) where the root node is the 1st element in the
list. The other nodes are in somewhat random order. The parentId refers
to the parent node.
I want to convert it into a list where the values are in pre-order.
I.e., I want to get this list as follows: ABCDEFGHIJ (see graph below).
I.e., get the 1st node, put in in the list. If it has children, go
through them one by one, get their child nodes, then put the parent in
the list, then the leftmost first, and go from there. I.e., so that
it's ordered in my linked list like this by (letters represent nodeId):
A
/ \
B J
/ | \
C H I
|
D
/|\
E F G
I created the following recursive method but it does not work
correctly. For example, it places the nodes A then B and then J into
the list first, rather than getting to J after adding all the child
nodes. "isOnTheList" checkes whether the item is already in the list.
"getImmediateChildren" returns the list of immediate child nodes
ordered by nodeId
Note: the empty list is passed to the method and is populated with the
result:
public static void orderTree(List list, List treeList) {
if(treeList == null || treeList.size() == 0)
return;
Node child = null; List children = null;
for(int i = 0; i < treeList.size(); i++) {
node = (Node) treeList.get(i);
// get list of children for this node
children = getImmediateChildren(node, treeList);
// if the node is not yet on the list, add it
if(! isOnTheList(node, list) )
list.add(cat);
// if it has children, recurse to add all other nodes
if(children.size() > 0) {
orderTree(list, children);
}
}
}
Any idea what the problem is?
Thanks.
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