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Index ‹ java-programmer
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- 1
- Mystery of the Shrinking JScrollPaneI've got a slight mystery that I can't fathom, and was wondering if someone
could help me understand what I've done wrong.
I'm trying to create a simple interface within a defined width and height.
It consists of a top half, and a bottom half.
The top half is a sideways-scrolling panel containing a bunch of smaller
panels side-by-side, in a GridLayout. This can expand to fit the width of
the overall UI, but must never take more height than it actually needs to
show the smaller panels in full.
The bottom half is simply a panel, which should absorb all extra height and
width.
If I add sufficient images to NOT exceed the width of the overall UI,
everything works as expected; the JScrollPane expands to fit the images'
height into its viewport, and the filler panel below takes up the slack.
But if I add another small panel, enough to exceed the width of the overall
UI, it goes wrong; the JScrollPane shrinks to practically nothing. I have
set the preferred height of the small panels and of the panel they sit in
(which is inside the scroll pane), so it's not as if it shouldn't be able to
figure out how tall it should be; after all, it figured it out when they
didn't exceed the width.
I just can't understand why it should suddenly shrink.
Here's an applet that will demonstrate the problem:
First, the HTML file to run it:
<HTML>
<HEAD>
<TITLE>TestShrinkingScrollPane</TITLE>
</HEAD>
<BODY>
<APPLET code="JTestShrinkingScrollPaneApplet.class" width="840"
height="640"></APPLET>
</BODY>
</HTML>
Now the single java source file to compile (compiling using 1.4.1_03),
JTestShrinkingScrollPaneApplet.java :
import javax.swing.JApplet;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;
import java.awt.GridLayout;
import java.awt.Insets;
/**
*
*/
/**
* @author Jason
*
*/
public class JTestShrinkingScrollPaneApplet extends JApplet
{
/**
*
*/
private static final long serialVersionUID = 1L;
public void init()
{
final int NUM_SMALL_PANELS = 5 ;
// Add a panel with GridBagLayout to the content pane as our root
component.
JPanel backPanel = new JPanel();
backPanel.setBackground(Color.RED);
backPanel.setLayout(new GridBagLayout() );
getContentPane().add(backPanel);
// Create our panel that will scroll sideways, and its contents.
JPanel scrollablePanel = new JPanel();
scrollablePanel.setBackground(Color.BLUE);
scrollablePanel.setLayout(new GridLayout(1, NUM_SMALL_PANELS, 0, 0) );
// No gaps between cells. Unlike FlowLayout(), this forces it on to one
row.
for (int panelIndex = 0 ; panelIndex < NUM_SMALL_PANELS ; panelIndex++)
{
JPanel smallPanel = new JPanel();
smallPanel.setBackground(Color.YELLOW);
smallPanel.setPreferredSize(new Dimension(160, 110) );
scrollablePanel.add(smallPanel);
}
// With no gaps between cells, the overall size needed is obvious:
scrollablePanel.setPreferredSize(new Dimension(160 * NUM_SMALL_PANELS,
110) );
// Create the bottom panel, that will absorb the extra height available.
JPanel fillerPanel = new JPanel();
fillerPanel.setBackground(Color.GREEN);
// Now create the grid bag.
GridBagConstraints constraints = new GridBagConstraints();
constraints.anchor = GridBagConstraints.CENTER ;
constraints.gridheight = 1 ;
constraints.gridwidth = 1 ;
constraints.gridx = 0 ;
constraints.insets = new Insets(0, 0, 0, 0);
constraints.ipadx = 0 ;
constraints.ipady = 0 ;
constraints.weightx = 1.0 ;
// The wide, scrollable panel - it can absorb the width, but must not
// absorb any more height THAN IT NEEDS!
constraints.fill = GridBagConstraints.HORIZONTAL ;
constraints.gridy = 0 ;
constraints.weighty = 0.0 ;
backPanel.add(new JScrollPane(scrollablePanel), constraints);
// The other panel - it can absorb the width AND the height.
constraints.fill = GridBagConstraints.BOTH ;
constraints.gridy = 1 ;
constraints.weighty = 1.0 ;
backPanel.add(fillerPanel, constraints);
}
}
If you compile and display it as it stands, you can see the JScrollPane is
quite rightly displaying the yellow small panels in full height.
If you now change NUM_SMALL_PANELS to 6, which goes beyond the width, and
then re-display it, you'll see the scroll pane collapses.
Any ideas as to why this happens? I've tried setting the viewport preferred
size but it doesn't make any difference. The best I can do is manually set
the scroll pane's size to the needed height + a scroll bar's preferred
height but that is neither elegant nor perfect - I want to know why it goes
wrong!
Any help on the why would be appreciated.
- 1
- How to open dialup connection in Java?Hi everyone,
Who know, how to open dialup connection from Java? (I found only one
way - to run another program (*.bat file), but it's not good idea). Any
another suggestions?
Haim.
- 3
- 3
- Grid Bag question.I am trying to put together a panel which needs to consist of 20 lines,
each containing :
JLabel - 2 columns
JTextField - 1 colomn
JTextField - 1 column
JLabel - 2 Columns
The JText fields would be filled out from arrays, so it would be layed
out with the help of a 'for' loop.
I put together a test program (provided below) to try to emulate this,
but the layout manager only seems to want to give each entity (JLabel,
JTextField) the same amount of width each regardless of what I specify
in the GridWidth fields. Can this be done with specifying sizes for the
individual JTextfields or labels? Please advise - Thanks - Lou
import java.awt.*;
import javax.swing.*;
public class Test_GridBag2 {
public static void addComponentsToPane(JPanel pane) {
JButton button;
JLabel label;
JTextField jtf;
pane.setLayout(new GridBagLayout());
GridBagConstraints c = new GridBagConstraints();
c.fill = GridBagConstraints.HORIZONTAL;
//pane.setPreferredSize(new Dimension(300,200));
for (int i = 0; i<3;i++)
{
label = new JLabel("test");
c.gridx = 0;
c.gridwidth = 2; //2 columns wide
c.gridy = i; //third row
c.weightx = 1.0;
//c.anchor = GridBagConstraints.EAST; //bottom of space
pane.add(label, c);
jtf = new JTextField();
c.gridx = 2; //aligned with button 2
c.gridwidth = 1; //2 columns wide
c.gridy = i;
c.weightx = 1.0; //request any extra vertical space
//c.anchor = GridBagConstraints.EAST;//third row
pane.add(jtf, c);
jtf = new JTextField();
c.gridx = 3; //aligned with button 2
c.gridwidth = 1; //2 columns wide
c.gridy = i;
c.weightx = 1.0; //request any extra vertical space
//c.anchor = GridBagConstraints.EAST;//third row
pane.add(jtf, c);
label = new JLabel("");
c.gridx = 4; //aligned with button 2
c.gridwidth = 2; //2 columns wide
c.gridy = i;
//c.insets = new Insets(0,0,0,10);
c.weightx = 1.0; //request any extra vertical space
//c.anchor = GridBagConstraints.EAST;//third row
pane.add(label, c);
}
}
private static void createAndShowGUI() {
JFrame frame = new JFrame("GridBagLayoutDemo");
JFrame.setDefaultLookAndFeelDecorated(true);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
JPanel panel = new JPanel();
addComponentsToPane(panel);
frame.getContentPane().add( panel );
//Display the window.
frame.pack();
frame.setVisible(true);
}
public static void main(String[] args) {
javax.swing.SwingUtilities.invokeLater(new Runnable() {
public void run() {
createAndShowGUI();
}
});
}
}
- 7
- Java regex imposture re: Perl regex compatibility// java has claimed to have added Perl style regular expressions ,
however
// writing a regular expression containing a variable is ugly in java.
// in Perl: $rec =~ s/$delimiter//g is easy to write and to read.
// in java: if delimiter may hold say "||" or "!" isntead of [a-z]
text,
// you have to quote it as below with preceding \\Q (not just \Q ) and
// trailing \\E. ugly and difficult to code!
rec = rec.replaceAll("\\Q" + delimiter + "\\E" ,"");
So even though java has perl style regex in principle, in practice,
in java they seem nearly unusable!
-A.C. Attlee
- 7
- HAVI packages, where?Hi everyone, I want to download HAVI API packages for java but i don't
know where can i download its. Thank you
- 8
- basics of ANThi, i have downloaded and started reading the ant tutorial.
i am confused becuase some of the concepts , the tutorial (jakarta )
is not making clear.
my objective is to compile and run a java program.
my questions are as follows
it is called in order to compile and run you need a "build.xml" file .
where is that file ?
QUESTION 1: is it within ant distribution OR i have to make a
build.xml file myself?
The tutorial does not say anything about it. it just starts straight
forward with a demo "build.xml" file.
where do i put this "build.xml" file ?
QUESTION 2 :
i have a java code here.
>md src
package oata;
public class HelloWorld {
public static void main(String[] args) {
System.out.println("Hello World");
}
}
location of this code is "src/oata/HelloWorld.java"
Now tell, where do i put "build.xml" file ?
- 8
- Pooling of connectionsHi all,
I've read a few articles about how pooled connections are more
efficient because you don't need to repeatedly setup/teardown a
connection - you just acquire connection from the pool.
Exactly what steps in setting up/tearing down a connection are skipped
by acquiring an already existing connection? Perhaps the steps in
establishing/tearing down a connection would help in answering this
question?
Thanks
Taras
- 8
- Java RPCHi All,
We have a set of application that communicates with embeded devices
that runs linux. Now we decide to use xml-rpc to send commands to the
devices with Apache's xmlrpc (or any other). We only need to generate,
and parse the structured xml string that contains the method name and
parameters. In other words we dont want to use a rpc server.
My question is how can I obtain the xml string of RPC command by only
suplying the method name and a vector that contains the parameters.
ps. In addition to primitive data types, parameters may contain
struct, array and etc.
Thanks in advance for your answer..
- 8
- Layout problem driving me insane - panels, resizing, etcIchBin wrote:
> email***@***.com wrote:
>>> Get NetBeans. (Get the latest one, 5.5) You don't need any plugins,
>>> everything is there for you already. Go through the tutorial below,
>>> it'll take about 30 minutes. If your eyes don't pop out of your head
>>> like Rodger Rabbit, then you can safely ignore it.
>>>
>>> http://www.netbeans.org/kb/50/quickstart-gui.html
>>
>> 60 MB - yikes. I'll download it tonight and play with it a little
>> bit... and also try all the other suggestions. I'll try and post my
>> conclusions tomorrow.
>>
[snip]
Just looked at the code again. It's ok but wanted to slim it down one
more time..
import java.awt.Dimension;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.BorderFactory;
import javax.swing.JButton;
import javax.swing.JComponent;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTable;
import javax.swing.JTextArea;
import javax.swing.ListSelectionModel;
import javax.swing.SwingUtilities;
import com.jgoodies.forms.builder.DefaultFormBuilder;
import com.jgoodies.forms.debug.FormDebugPanel;
import com.jgoodies.forms.debug.FormDebugUtils;
import com.jgoodies.forms.factories.ButtonBarFactory;
import com.jgoodies.forms.layout.FormLayout;
public class LayoutProblem implements ActionListener
{
public static void main(String[] args)
{
SwingUtilities.invokeLater(new Runnable()
{
public void run()
{
new LayoutProblem();
}
});
}
public LayoutProblem()
{
jFrame.setDefaultCloseOperation(jFrame.EXIT_ON_CLOSE);
jFrame.add(buildMainPanel());
jFrame.setPreferredSize(new Dimension(475,600));
jFrame.pack();
jFrame.setVisible(true);
}
private JPanel buildMainPanel()
{
FormLayout layout = new FormLayout (
/* Columns */ "default:grow",
/* Rows */ "pref, 12dlu, fill:0:grow(0.50), 20dlu,
fill:0:grow(0.50)"
);
DefaultFormBuilder builder = DEBUGMODE
? new DefaultFormBuilder(layout,new FormDebugPanel())
: new DefaultFormBuilder(layout);
builder.setDefaultDialogBorder();
builder.nextLine(2);
builder.append(buildControl(jTable));
builder.append(buildButtonBar());
builder.append(buildControl(jTextArea));
if (DEBUGMODE)
{
FormDebugUtils.dumpAll(builder.getPanel());
}
return builder.getPanel();
}
private JComponent buildButtonBar()
{
JPanel jPanel = new JPanel();
jPanel = ButtonBarFactory.buildCenteredBar(
buildControl(BUTTON1),
buildControl(BUTTON2),
buildControl(BUTTON3),
buildControl(TEXT_EXIT));
jPanel.setBorder(BorderFactory.createRaisedBevelBorder());
return jPanel;
}
private JButton buildControl(String labelText)
{
jButton = new JButton(labelText);
jButton.addActionListener(this);
return jButton;
}
private JComponent buildControl(JTable jTable)
{
jTable = new JTable(dataValues, columnNames);
JScrollPane scrollPane = new JScrollPane(jTable);
jTable.setSelectionMode(ListSelectionModel.SINGLE_SELECTION);
return scrollPane;
}
private JComponent buildControl(JTextArea jTextArea)
{
jTextArea = new JTextArea(logAreaHdr);
JScrollPane scrollPane = new JScrollPane(jTextArea );
return scrollPane;
}
public void actionPerformed(ActionEvent e)
{
final String method = "jBotton_actionPerformed(ActionEvent " +
e + "): ";
if (DEBUGMODE)
{
System.out.println(DEBUGHEATER + method);
}
if (BUTTON1.equals(e.getActionCommand()))
{
}
else if (BUTTON2.equals(e.getActionCommand()))
{
}
else if (BUTTON3.equals(e.getActionCommand()))
{
}
else if (TEXT_EXIT.equals(e.getActionCommand()))
{
System.exit(0);
}
}
private static final String PROGRAM = (((new
Throwable()).getStackTrace())[0].getClassName())+".";
private static final String DEBUGHEATER = "( DEBUG ) " + PROGRAM;
private static final boolean DEBUGMODE = false;
private JFrame jFrame = new JFrame("JGoodies
Forms Layout Demo");
private JTable jTable;
private JTextArea jTextArea;
private JButton jButton;
private final String BUTTON1 = "Button 1";
private final String BUTTON2 = "Button 2";
private final String BUTTON3 = "Button 3";
private final String TEXT_EXIT = "EXIT";
private final String logAreaHdr =
"---------------------------\n---------------------------\n---------------------------\n";
private final String columnNames[] = {"Column 1", "Column
2", "Column 3"};
private String dataValues[][] = {
{"0aa", "bbb", "ccc"},
{"0dd", "eee", "fff"},
{"0gg", "hhh", "iii"},
{"1aa", "bbb", "ccc"},
{"1dd", "eee", "fff"},
{"1gg", "hhh", "iii"},
{"2aa", "bbb", "ccc"},
{"2dd", "eee", "fff"},
{"2gg", "hhh", "iii"},
{"3aa", "bbb", "ccc"},
{"3dd", "eee", "fff"},
{"3gg", "hhh", "iii"},
{"4aa", "bbb", "ccc"},
{"4dd", "eee", "fff"},
{"4gg", "hhh", "iii"},
{"5aa", "bbb", "ccc"},
{"5dd", "eee", "fff"},
{"5gg", "hhh", "iii"},
{"6aa", "bbb", "ccc"},
{"6dd", "eee", "fff"},
{"6gg", "hhh", "iii"},
{"7aa", "bbb", "ccc"},
{"7dd", "eee", "fff"},
{"7gg", "hhh", "iii"},
{"8aa", "bbb", "ccc"},
{"8dd", "eee", "fff"},
{"8gg", "hhh", "iii"},
{"9aa", "bbb", "ccc"},
{"9dd", "eee", "fff"},
{"9gg", "hhh", "iii"},
{"aaa", "bbb", "ccc"},
{"ddd", "eee", "fff"},
{"ggg", "hhh", "iii"},};
}
--
Thanks in Advance...
IchBin, Pocono Lake, Pa, USA
http://weconsultants.servebeer.com/JHackerAppManager
__________________________________________________________________________
'If there is one, Knowledge is the "Fountain of Youth"'
-William E. Taylor, Regular Guy (1952-)
- 8
- Java in AT&T PWPHi,
I was referred to you because I'm having a problem getting this to run in
AT&T PWP (Personal Web Pages). I compile the Java Program using NetBeans
IDE 3.6. I upload the .java, the .class and the .html files to my PWP
library.
import java.awt.*;
import java.applet.*;
import javax.swing.*;
public class AppHelloWorld extends JApplet
{
public void init()
{
resize(700,100);
}
public void paint(Graphics g)
{
g.drawString("Hello, Applet world!", 10, 25);
}
}
---------------------------------------------------------------
This is the page I run in the browser (Internet Explorer and Netscape).
<HTML>
<HEAD>
<TITLE>Applet HTML Page</TITLE>
</HEAD>
<BODY>
<H3><HR WIDTH="100%">Applet HTML Page<HR WIDTH="100%"></H3>
<P>
<APPLET code="AppHelloWorld.class" width=350 height=200>
</APPLET>
</P>
<HR WIDTH="100%"><FONT SIZE=-1><I>Generated by NetBeans IDE</I></FONT>
</BODY>
</HTML>
This is the message I get from the browser:
java.lang.ClassFormatError: AppHelloWorld (Extra bytes at the end of the
class file)
The page will run in Edit*Plus and IE (FILE, OPEN, BROWSE) and Netscape
(FILE, OPEN FILES, select document).
Can you provide any information on how to get this to run in the browsers?
Wayne Rawls
- 9
- Good programming questionI was just wondering as to what is a better standard to program by. If
I have a class like this:
class MyClass {
private int myVariable;
private void myMethod1(){
myVariable = 1;
}
private void myMethod2(){
this.myVariable = 1;
}
}
Which method is better? Is there a better choice? Does it make any
difference which way I do it? Maybe this sounds like an insignificant
question but I have done this both ways and just don't know if there is
a good reason to go one way or the other.
- 9
- Shuffled Poker DeckHi all,
Im new to Java, and as Training for me I tried to build an Application,
which returns a shuffled Pokerdeck. (Random from 1 to 52)
Maybe you will laugh, but i needed a whole day to solve it, and I think its
even not good solution.
Well, at least it works, but please could you give me a hint, how to solve
this problem easier.
Heres the code:
/**
* @(#)Poker.java
*
*
* @author Martin Krainer
* @version 1.00 2007/1/22
*/
public class Poker {
static int[] deck = new int[52];
void buildDeck() { // builds a deck with 52
(hopefully) different Integers
for (int i=0; i<52; i++) {
deck[i] = (int)(Math.random()*10E7);
}
}
void shuffledDeck(int[] a) { // now here I tried hard and
long to get a field with numbers from 1 to 52
long[] zahl= new long[52];
for (int i=0; i<10E7; i++) {
for (int j=0; j<52; j++) {
if (i == deck[j]) {
zahl[j] = j;
System.out.print( " " + (zahl[j]+1) );
}
}
}
}
public static void main(String[] args) {
Poker p = new Poker();
p.buildDeck();
p.shuffledDeck(deck); //well, it works, but...
what do you think?
}
}
- 11
- checking for org.omg.CORBA.OBJECT_NOT_EXISTHi,
I'm writing a java CORBA client, using the Visibroker ORB. Sometimes
when I call methods on the remote object references I get the following
exception
org.omg.CORBA.OBJECT_NOT_EXIST: vmcid: OMG minor code: 0 completed:
No
Is there some way that I can check beforehand whether this exception
will be thrown, i.e. whether the remote object still exists? I thought
that I could do it like this:
if (myRef._non_existent()) {
// get a new myRef
}
myRef.doRemoteMethod();
But I've found that _non_existent() throws exceptions. Is there a
better way to check for the state that causes an OBJECT_NOT_EXIST
exception?
Regards,
Dan
- 16
- Torque and WebsphereWe are implenting a J2EE project where WebSphere is handling
connection pooling for the application calls to a database. We have a
JDBC Resource configured which tested successfully. We also have the
application successfully connecting to the database which is confirmed
by the following error message.
rethrown as org.apache.torque.TorqueException: [IBM][CLI Driver][DB2]
SQL0204N "TSTUSER.PERMISSION" is an undefined name.
The problem is apparent, TSTUSER does not own a table called
PERMISSION and in fact this table is owned by the user TELUSER and our
intention is for TSTUSER to execute DML against it. We have not been
able to configure the schema.xml file nor the build.properties to
instruct Torque to produce SQL that fully qualifies the object name
with the appropriate schema owner. Any advice you might offer will be
appreciated.
Best regards
|
| Author |
Message |
christian.bongiorno
|
 Posted: 2006-8-11 11:59:00 |
Top |
java-programmer, polymorphic voodoo?
Ok, here is what I am trying to decipher. I have the following code
private void someMethod() {
ArrayList list1 = null;
LinkedList list2 = null;
cleverFunction(list1,list2);
}
private void cleverFunction(List first, List second) {
System.out.println("Static type for first is " + .....);
System.out.println("Static type for second is " + .....);
}
Ok, so, given a polymorphic call like this, is it possible, through
whatever witchcraft necessary, to determine what the static types of
the type polymorphic parameters are?
Maybe some sort of interrogation of the stack? Maybe some sorta
reflection?
Ideas?
christian
http://christian.bongiorno.org/resume.PDF
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Chris Smith
|
| Posted: 2006-8-11 13:10:00 |
Top |
java-programmer >> polymorphic voodoo?
<email***@***.com> wrote:
> Ok, here is what I am trying to decipher. I have the following code
>
> private void someMethod() {
> ArrayList list1 = null;
> LinkedList list2 = null;
>
> cleverFunction(list1,list2);
>
> }
>
> private void cleverFunction(List first, List second) {
> System.out.println("Static type for first is " + .....);
> System.out.println("Static type for second is " + .....);
> }
>
> Ok, so, given a polymorphic call like this, is it possible, through
> whatever witchcraft necessary, to determine what the static types of
> the type polymorphic parameters are?
You always know the static types of variables. In this case, the static
type of both 'first' and 'second' is java.util.List.
Did you want to know the static types of the actual parameters in the
calling stack frame? In that case, things get harder. You'd need to
have access to either debugging information or the source code for the
calling function, since the information you're looking for is partially
lost during the translation to bytecode.
Let me make the obligatory statement that if you care, your design has
probably gone horribly wrong.
--
Chris Smith - Lead Software Developer / Technical Trainer
MindIQ Corporation
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EJP
|
| Posted: 2006-8-11 14:19:00 |
Top |
java-programmer >> polymorphic voodoo?
Chris Smith wrote:
> Did you want to know the static types of the actual parameters in the
> calling stack frame? In that case, things get harder.
Err, first.getClass()? second.getClass()?
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Michael Rauscher
|
| Posted: 2006-8-11 16:21:00 |
Top |
java-programmer >> polymorphic voodoo?
EJP schrieb:
> Chris Smith wrote:
>> Did you want to know the static types of the actual parameters in the
>> calling stack frame? In that case, things get harder.
>
> Err, first.getClass()? second.getClass()?
Err, NullPointerException? ;)
Bye
Michael
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ram
|
| Posted: 2006-8-11 16:32:00 |
Top |
java-programmer >> polymorphic voodoo?
email***@***.com writes:
>System.out.println("Static type for first is " + .....);
>System.out.println("Static type for second is " + .....);
>[...] is it possible [...] to determine [...] the static types
>of the [...] [arguments]?
Not really, but here is an approximation that might work
sometimes:
public class Main
{
static void printStaticTypesOfExpressions
( final java.util.ArrayList first,
final java.util.ArrayList second )
{ System.out.println( "java.util.ArrayList" );
System.out.println( "java.util.ArrayList" ); }
static void printStaticTypesOfExpressions
( final java.util.LinkedList first,
final java.util.ArrayList second )
{ System.out.println( "java.util.LinkedList" );
System.out.println( "java.util.ArrayList" ); }
static void printStaticTypesOfExpressions
( final java.util.ArrayList first,
final java.util.LinkedList second )
{ System.out.println( "java.util.ArrayList" );
System.out.println( "java.util.LinkedList" ); }
static void printStaticTypesOfExpressions
( final java.util.LinkedList first,
final java.util.LinkedList second )
{ System.out.println( "java.util.LinkedList" );
System.out.println( "java.util.LinkedList" ); }
public static void main( final java.lang.String[] args )
{ final java.util.ArrayList list1 = null;
final java.util.LinkedList list2 = null;
printStaticTypesOfExpressions( list1, list2 ); }}
java.util.ArrayList
java.util.LinkedList
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Paul Davis
|
| Posted: 2006-8-11 22:25:00 |
Top |
java-programmer >> polymorphic voodoo?
Stefan Ram wrote:
> email***@***.com writes:
> >System.out.println("Static type for first is " + .....);
> >System.out.println("Static type for second is " + .....);
> >[...] is it possible [...] to determine [...] the static types
> >of the [...] [arguments]?
>
> Not really, but here is an approximation that might work
> sometimes:
>
> public class Main
> {
> static void printStaticTypesOfExpressions
> ( final java.util.ArrayList first,
> final java.util.ArrayList second )
> { System.out.println( "java.util.ArrayList" );
> System.out.println( "java.util.ArrayList" ); }
>
> static void printStaticTypesOfExpressions
> ( final java.util.LinkedList first,
> final java.util.ArrayList second )
> { System.out.println( "java.util.LinkedList" );
> System.out.println( "java.util.ArrayList" ); }
>
> static void printStaticTypesOfExpressions
> ( final java.util.ArrayList first,
> final java.util.LinkedList second )
> { System.out.println( "java.util.ArrayList" );
> System.out.println( "java.util.LinkedList" ); }
>
> static void printStaticTypesOfExpressions
> ( final java.util.LinkedList first,
> final java.util.LinkedList second )
> { System.out.println( "java.util.LinkedList" );
> System.out.println( "java.util.LinkedList" ); }
>
> public static void main( final java.lang.String[] args )
> { final java.util.ArrayList list1 = null;
> final java.util.LinkedList list2 = null;
> printStaticTypesOfExpressions( list1, list2 ); }}
>
> java.util.ArrayList
> java.util.LinkedList
Issue being, the method called from main is determined at compile time
as revealed by javap:
public static void main(java.lang.String[]);
Code:
0: aconst_null
1: astore_1
2: aconst_null
3: astore_2
4: aload_1
5: aload_2
6: invokestatic #42; //Method
printStaticTypesOfExpressions:(Ljava/util/ArrayList;Ljava/util/LinkedList;)V
9: return
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Chris Smith
|
| Posted: 2006-8-11 22:44:00 |
Top |
java-programmer >> polymorphic voodoo?
EJP <email***@***.com> wrote:
> Chris Smith wrote:
> > Did you want to know the static types of the actual parameters in the
> > calling stack frame? In that case, things get harder.
>
> Err, first.getClass()? second.getClass()?
You're confusing type with class. As Michael pointed out, the values of
these variables in the example are null, so they don't point to any
objects and it won't work to ask for the object's class. Even if they
weren't null, though, getClass() would be the wrong answer. That would
tell you the class of the object, and not the type of the variable that
points to it.
As I said earlier, the types of the formal parameters are both
java.util.List. Any other answer is wrong. The types of the actual
parameters in the example given here are java.util.ArrayList and
java.util.LinkedList. This would remain true even if the object pointed
to were of class javax.management.AttributeList (a class that extends
ArrayList). That still wouldn't change the type of the variable.
It's worth mentioning that if one wants to know static types of the
actual parameters out of a small set of options, then method overloading
can do it. Since static types are, by definition, known at compile-
time, this should be sufficient... but only if there's only a small set
of options; otherwise, it becomes impractical or impossible.
--
Chris Smith - Lead Software Developer / Technical Trainer
MindIQ Corporation
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Oliver Wong
|
| Posted: 2006-8-12 4:15:00 |
Top |
java-programmer >> polymorphic voodoo?
"Paul Davis" <email***@***.com> wrote in message
news:email***@***.com...
>
> Stefan Ram wrote:
>> email***@***.com writes:
>> >System.out.println("Static type for first is " + .....);
>> >System.out.println("Static type for second is " + .....);
>> >[...] is it possible [...] to determine [...] the static types
>> >of the [...] [arguments]?
>>
[code snipped]
>
> Issue being, the method called from main is determined at compile time
Which is fine, because the static types are also known at compile time.
- Oliver
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Paul Davis
|
| Posted: 2006-8-16 1:53:00 |
Top |
java-programmer >> polymorphic voodoo?
Oliver Wong wrote:
> "Paul Davis" <email***@***.com> wrote in message
> news:email***@***.com...
> >
> > Stefan Ram wrote:
> >> email***@***.com writes:
> >> >System.out.println("Static type for first is " + .....);
> >> >System.out.println("Static type for second is " + .....);
> >> >[...] is it possible [...] to determine [...] the static types
> >> >of the [...] [arguments]?
> >>
> [code snipped]
> >
> > Issue being, the method called from main is determined at compile time
>
> Which is fine, because the static types are also known at compile time.
>
> - Oliver
True but, I've (unfortuneately) seen more than a few cases where
someone thinks it will happen at runtime
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christian.bongiorno
|
| Posted: 2006-8-17 2:39:00 |
Top |
java-programmer >> polymorphic voodoo?
It's mostly academic. I have even thought about going so far as to load
the actual class bytes and interrogate them. Later posts have suggested
what I think is most likely: A Debugger.
I am off the project now where I might have used something like this,
but still think about what I might have done.
> Let me make the obligatory statement that if you care, your design has
> probably gone horribly wrong.
>
> --
> Chris Smith - Lead Software Developer / Technical Trainer
> MindIQ Corporation
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Index ‹ java-programmer |
- Next
- 1
- I only invest in Jeff Relf.Hi Hot Tamales !,
You related another gem ( What a guy ),
" Internet and technology stocks
have netted me a loss of approximately 20%.
FCEL, my one energy investment,
has netted me a gain of 20%.
I think Energy
( cells, hydrogen, renewable, even nuclear )
are the next wave. "
The value of FCEL didn't go up,
the value of the dollar,
( i.e. the stock of the U.S. government ), went down.
I only invest in Jeff Relf, not that I'm doing any better.
- 2
- What it the type of the Class without modifierRoedy Green <email***@***.com> wrote:
> This is one of my pet peeves . It does not have a name. It is
> referred to with religious reverence by an indirect name "default"
> which tells you where in is used. Some heretics dare name it
> "package".
Hey, are you calling me a heretic?!? :)
--
www.designacourse.com
The Easiest Way To Train Anyone... Anywhere.
Chris Smith - Lead Software Developer/Technical Trainer
MindIQ Corporation
- 3
- Servlet HelpDear Friends
pls help in running servlet in Tomcat. i m not getting which setting
should i do for it.
pls send me how to execute a servlet HalloWorld
paresh
- 4
- Text/Console mode UIHi All,
is there anything like swing but working in text mode? I need a simple
user interface working in the console mode for my little app.
thanks
schw
- 5
- Need help in validating the period in an email address. (new Java student)I am a new Java student and would appreciate a little help.
What I need is to be able to validate the period as the fourth from
the last character in an email address and return focus if the address
is invalid. The best I have been able to do is a good address on the
first attempt. If an incorrect address is entered first I am unable to
get it to accept a good address from then on. The code below is what I
have left after removing everything that did not work.
Is there anyone here that can provide some assistance. Thanks
// validate the e-mail
var RegeMail=document.Register.eMail.value
var atSign = RegeMail.indexOf("@")
if (RegeMail == " " || atSign == -1) {
alert("Please enter your e-mail address")
document.Register.eMail.value = " "
document.Register.eMail.focus()
}
- 6
- Classes generated by eclipse vs javac have different serialVersionUIDHi,
I'm using eclipse 3.2 for development and have configured my project to
use JDK 1.5.0_07 with Compiler compliance level 1.3 (using default
compliance settings) and selected all "Classfile Generation" options
except "Inline finally blocks." The problem I'm having is that the
class files that are generated by eclipse are not the same as those
generated by javac (also using JDK 1.5.0_07), which is used in a make
script. javac is invoked like so:
javac -source 1.3 -g -d classes -nowarn -deprecation -classpath
<classpath> ...
The different class files cause a problem because I have serialized
some objects already with the javac classes so when I try to
deserialize them with the eclipse classes, I get the
InvalidClassException. When I run serialver on the offending class
file, I get two different values for the class file generated with
javac and the one generated using eclipse.
Has anyone ever had this or some similar problem? How do I correct this
(besides not using the eclipse class files)? I've spent many hours
scouring the web to find a solution, but have had no success. Any help
would be really appreciated!
Thanks,
Tai
- 7
- XMLencoder customHey all,
I'm using XML encoder for long term storage. However, I'd like to be
able to customize what is saved at runtime. Why? There are several
data structures, which can balloon the size of the file to a few
megabytes. This data is not something every user might want to save
on load. I'd like to give them the option of whether or not to encode
these particular data structures. The rest of the code is perfectly
capable to dealing with these structures set to null. They often are
null.
I was thinking the easiest way for me to do this would be as follows:
I know this is not XMLEncoder code (but java serialization type
code...but that's what I need help with :) ) I have a feeling this is
going into the realm of persistance delegates, but I really have no
idea.
private Hashtable details= null;
private void writeObject(ObjectOutputStream s) throws IOException
{
if( dontSaveDetails)
{
Hashtable detailsBackup = details;
//clear the details, so they're not saved
setDetails(new Hashtable());
s.defaultWriteObject();
//restore details for the current session
details = bckdetails;
}
else
{
s.defaultWriteObject();
}
}
Any ideas on how to put this logic into the XMLencoder world?
Thanks,
Ymain
- 8
- [OT] Teaching OO / Java (was: Concentric Circles Loosing It)Hi !
"Anthony Borla" wrote:
>
> "Alan P" <email***@***.com> wrote in message
> news:br0efp$ola$email***@***.com...
> >
> > I'm a newbie Java student as well, and AFAIK we all start
> > the same way -> by using a 'Turtle' class. Remember those
> > little robot things from infant school, with the penUp(),
> > penDown() etc.
> >
> > The idea is not stunning effects, but an introduction to OOPS
[...]
> I'm just a very firm believer [based mainly anectdotal, not statistical,
> evidence] in teaching programming concepts from first principles which, to
> me, means:
>
> * Teaching the rudiments of console windows / command-line
> usage, which includes the use of editors, compilers, and similar
> tools.
O.k., this is meant to teach the "DE" (leaving out the leading 'I'). But
maybe some people want their students to concentrate on the course theme, so
they decide to use an IDE. Personally, I think one has to know how to deal
with a language without any external (!) IDE, so you should know about
"javac" and "java"...
>
> Taking a Windows environment as an example, all that is needed
> is knowing how to:
>
> - Open up a Command Window
> - Load and use Notepad [or one of its more versatile
> replacements]
> - Invoke javac.exe and java.exe
>
> * Teaching language syntax basics using a serial execution
> programming model, a fancy description for a program
> which executes by starting at point A and proceeding
> downwards towards towards point B e.g.
>
> ...
> public static void main(String[] args)
> {
> // Point A
> ...
> ...
> // Point B
> }
> ...
>
> Once students have grasped the basics of structured / object-based
> programming, all in a serial, non-GUI enviroment, the rudiments of OOP
> [inheritance, polymophism] can be taught.
This will teach students to write programs the serial way first. In my
opinion, it would be the better approach to teach basic OO concepts first
(before even invoking an editor for the first time, maybe using some
pseudo-language).
Using your approach, students would learn how to write an imperative program
frist (one big main() method). Then you would introduce a completely new
paradigm, the structured programming, using functions (other than the main()
method, but still implementing a single class). Later on, you would
introduce yet another paradigm, the object-oriented programming implementing
specialized classes which will focus on certain tasks.
Have you ever tried to teach oo concepts to a - let's say - COBOL programmer
(nothing to say against COBOL programmer, of course, replace with almost any
3GL you (don't) like)? You will have a very hard time unless he (or she)
will understand them, because the imperative paradigm will block their view
onto objects. So I would always prefer to teach the object-oriented way
first. For most people, it will be quite easy to write "one big main()
method" if they are forced to do it, and the oo paradigm will not stand in
their way.
> Once these basics have been
> mastered, the next steps could be taken, which would probably be one, or
> more, of the following:
>
> * Algorithms / Data Structures
Data Structures might well be renamed "Object Oriented Design"... ;-)
> * Concurrent / Advanced Programming
> * Event-driven / GUI Programming
>
> I guess you would describe me as decidedly 'old school' in this regard :)
!
>
> In a nutshell, I'm not comfortable with the notion that GUI's and graphics
> simplify the teaching of very important, fundamental programming ideas,
but
> I probably hold a minority opinion here.
>
> Programming, like mathematics, can be an exciting field. However, much
> effort, most of it in mundane areas, must be expended to satisfactorily
> grasp the basics on which all further learning progress rests. I can
> appreciate course designers wanting to make programming more interesting
or
> accessable, hence the use of GUI's and similar tools, or presenting ideas
in
> graphical form. IMO, though, it is best to avoid such things as they sport
> hidden complexities, and keep things as simple as possible, at least until
a
> firm grounding in the basics has been obtained.
Yes. But one might define "basics" somewhat different. You must not have (I
might even say "should not have") any knowledge about "serial" or
"functional" programming to learn to write good OO programs.
(O.k., I might have started another thread on this, but then...)
Cheers,
Michael
- 9
- Writing ASCII for r-232 output into induction machine??I have a machine that uses induction to bond metals together. The
machine has a remote heat station that you set the wattage, and the
time, etc (with up and down buttons) and it will run on its own.
However, every time I need to bond different metals, thicknesses,
widths, etc... I need to reset the info and go through the whole
process again. The machine, has an rs-232 port on the back of it,
which will accept codes written in ascii that will send that pertinent
information to it. I would like some help (Im an ascii newbie) with
writing these programs, so that I can store all the metals,
thicknesses, etc in a laptop connected to this remote heat station, and
then I can have anyone run it so long as they can read.
Any help would be greatly appreciated
Scott
PLEASE email me at email***@***.com
- 10
- Maximum number of ThreadsI'm developing a simple Java client that runs over a CORBA server.
The main client thread is waiting for notification from this server.
On each notification,
The client creates a new thread executing some logic with the server and close.
Each session spend most of the time waiting for the server.
At most there can be ~1000 open session.
My questions are:
1. How many threads can be open at the same time
(with response time of up to ~1 second)?
2. Does the JVM open a native thread for each java thread?
I know both question is OS and JVM dependent,
so I'm not expecting exact numbers here. The client will probably run on Solaris or NT.
Thanks.
- 11
- Need server-side solution to linking in framesDear all,
I am doing some maintainance in a JSP website which has been built
using frames (and I cannot remove that unfortunately).
So, I have 4 frames (top, and 3 vertical frames underneath the top).
The frame on the left is supposed to be for navigation, but when I
click on some navigation items, I am enforced to set the target to the
own navigation frame, because I need to do some other processing
(which I cannot avoid), and in the end I am using some javascript code
to change the location of the center frame (which in an ideal case
would be the target of the link on the navigation).
Does anyone know a way to avoid the javascript? Is there anyway that I
can load 2 different urls in 2 different frames via a single link? The
first URL is just a different set of parameters to the navigation
menu, and the second URL is the target of the navigation.
Best regards,
Pablo
- 12
- Raymond on Sun's strangleholdanoncoward wrote:
> JTK wrote:
>
>>> This made me think of an issue that has kicked around in my head for a
>>> whle. Just to be clear, IANAL. However, I seem to remember that one
>>> requirement of a patent be that the needed to be non-obvious to a
>>> skilled practitioner. Does someone know if this is correct?
>>
>>
>> Correct but irrelevant. Money talks, justice walks. If Sun wants to
>> shut down a Java implementation, all they need to do is litigate it to
>> death.
>
> How about Mono and .NET. Microsoft has patented the whole lot.
> Mono is *massively* infringing on copyrighted and patented Microsoft IP.
> What's your word on that?
Why would I have a "word on that", especially in a Java forum? You're
the one who love C# so much, you tell us why you prefer it to Java!
- 13
- Changing the Background Color for One Cell in a JTableI've been working on this for a few hours. I've read tutorials and seen
different examples, but this is still driving me nuts.
I have a table and want to be able to change the color of one cell in it.
It seems to do this, I can't get a cell renderer and just change the color,
I have to create my own class to do that. I've tried that and a number of
other things and can't get it to work.
I finally took the SimpleTableDemo from Sun and checked to make sure it was
running. Once it was, I added four lines:
boolean isSelected = table.isCellSelected(1, 1);
DefaultTableCellRenderer defRender = (DefaultTableCellRenderer)
table.getCellRenderer(1, 1);
Component cellRenderer = defRender.getTableCellRendererComponent(table,
"Huml", isSelected, false, 1, 1);
cellRenderer.setBackground(Color.blue);
(The whole example is at the bottom of this post.)
When I use this example, it turns ALL the cells in the table blue, not just
the one at 1,1.
I've got several questions about this:
1) Do I have to create my own cell renderer to change a cell background
color, or can't I just do it like above? Even when I used my own renderer,
I still got the actual Component named cellRenderer using the same
parameters, so what difference would doing it in a separate class make?
2) The renderer needs the value that is in the cell currently. In my own
program, I got that from the DefaultTableModel I was using. Here I just
used the text that was put in that cell. Is there any way to get the cell
value directly from the table? In this example, I tried getting a
DefaultTableModel (by casting) from the table, but it didn't work, so I
couldn't get the data by reading the cell.
3) Why does this code (above) set the entire table and not just the cell at
1,1?
If anyone has a simpler example of how to set the background color in just a
few lines, I'd be glad to see it. I can't believe how much I need to do
just to change the background color in one table cell!
Thanks for any help/insight!
Hal
----------------example code----------------
/*
* SimpleTableDemo.java requires no other files.
*/
import java.awt.Color;
import java.awt.Component;
import java.awt.Dimension;
import java.awt.GridLayout;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTable;
import javax.swing.table.DefaultTableCellRenderer;
import com.hal.gui.HalCellRenderer;
public class SimpleTableDemo extends JPanel {
private boolean DEBUG = false;
public SimpleTableDemo() {
super(new GridLayout(1,0));
String[] columnNames = {"First Name",
"Last Name",
"Sport",
"# of Years",
"Vegetarian"};
Object[][] data = {
{"Mary", "Campione",
"Snowboarding", new Integer(5), new Boolean(false)},
{"Alison", "Huml",
"Rowing", new Integer(3), new Boolean(true)},
{"Kathy", "Walrath",
"Knitting", new Integer(2), new Boolean(false)},
{"Sharon", "Zakhour",
"Speed reading", new Integer(20), new Boolean(true)},
{"Philip", "Milne",
"Pool", new Integer(10), new Boolean(false)}
};
final JTable table = new JTable(data, columnNames);
table.setPreferredScrollableViewportSize(new Dimension(500, 70));
// table.setFillsViewportHeight(true);
if (DEBUG) {
table.addMouseListener(new MouseAdapter() {
public void mouseClicked(MouseEvent e) {
printDebugData(table);
}
});
}
//Create the scroll pane and add the table to it.
JScrollPane scrollPane = new JScrollPane(table);
//Add the scroll pane to this panel.
add(scrollPane);
//======================================================
//Only part I have added is the next four lines
//======================================================
boolean isSelected = table.isCellSelected(1, 1);
DefaultTableCellRenderer defRender = (DefaultTableCellRenderer)
table.getCellRenderer(1, 1);
Component cellRenderer =
defRender.getTableCellRendererComponent(table, "Huml", isSelected, false,
1, 1);
cellRenderer.setBackground(Color.blue);
}
private void printDebugData(JTable table) {
int numRows = table.getRowCount();
int numCols = table.getColumnCount();
javax.swing.table.TableModel model = table.getModel();
System.out.println("Value of data: ");
for (int i=0; i < numRows; i++) {
System.out.print(" row " + i + ":");
for (int j=0; j < numCols; j++) {
System.out.print(" " + model.getValueAt(i, j));
}
System.out.println();
}
System.out.println("--------------------------");
}
/**
* Create the GUI and show it. For thread safety,
* this method should be invoked from the
* event-dispatching thread.
*/
private static void createAndShowGUI() {
//Create and set up the window.
JFrame frame = new JFrame("SimpleTableDemo");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
//Create and set up the content pane.
SimpleTableDemo newContentPane = new SimpleTableDemo();
newContentPane.setOpaque(true); //content panes must be opaque
frame.setContentPane(newContentPane);
//Display the window.
frame.pack();
frame.setVisible(true);
}
public static void main(String[] args) {
//Schedule a job for the event-dispatching thread:
//creating and showing this application's GUI.
javax.swing.SwingUtilities.invokeLater(new Runnable() {
public void run() {
createAndShowGUI();
}
});
}
}
- 14
- 15
- Paramaters in EL?Hi All!
Is it possible to do this:
<%String deptName = (String)request.getParameter("deptName");
Department dept = org.getDepartment(deptName); %>
With just c:set or jsp:useBean tags?
Rob
:)
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