createImage() always returns null
I want to create an off-screen image in a Swing application.
The program compiles without errors, but createImage() always
returns null.
The only examples from the tutorial that contain createImage() are
applets (not swing applications) and seem to work fine.
For verification, I included the relevant code snippet (as shown
below) in a swing application example from the tutorial -- same
result.
Am I missing something??? or is that a swing bug?
I am using jdk117_v1a, swing-1.1.1-beta1
--8><
// extracted from ".../tutorial/ui/swingComponents/example-swing/"
public class ScrollDemo extends JPanel
{
:
:
public ScrollDemo()
{
:
:
//
Image offScrImage = createImage(100,100);
if (offScrImage == null)
System.err.println("createImage() returns null!");
JPanel offScrPanel2 = new JPanel();
Image offScrImage2 = offScrPanel2.createImage(100,100);
if (offScrImage2 == null)
System.err.println("createImage() returns null!");
//
:
:
}
}
--8><
$ java ScrollDemo
createImage() returns null!
createImage() returns null!
--8><
Any feedback appreciated
--
Manfred
Re: createImage() always returns null
Hello,
is the Panel already visible?
If not, then show() it before getting a Image!
greetings
Chris
Manfred Bartz wrote:
>
> I want to create an off-screen image in a Swing application.
> The program compiles without errors, but createImage() always
> returns null.
>
> The only examples from the tutorial that contain createImage() are
> applets (not swing applications) and seem to work fine.
>
> For verification, I included the relevant code snippet (as shown
> below) in a swing application example from the tutorial -- same
> result.
>
> Am I missing something??? or is that a swing bug?
> I am using jdk117_v1a, swing-1.1.1-beta1
...
>
> Any feedback appreciated
> --
> Manfred
--
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String email= "mailto:[EMAIL PROTECTED]";
String SMSMail = "mailto:[EMAIL PROTECTED]?Subject=SMS: info";
URL homepage = new URL("http://www.tu-chemnitz.de/~chu/");
Talktalkto = new Talk("[EMAIL PROTECTED]");
Integer ePlus= new Integer(4628555);
}
Problem : can't find class
Hello, I am having the following problem when I try to execute a java program , says : can't find class test This happens although the file test.class and test.java are in the same directory from where I am executing java. I am however able to compile java programs without any problems. Also I can run servlets through the browser. The classpath variable is as follows : CLASSPATH=/usr/local/java/lib/classes.zip:/usr/local/java/jsdk/lib/jsdk.jar I am using Red Hat Linux 5.0 and jdk1.1.5. I know its some silly problem but unable to figure it out. Quote of the day ... ** When Depression strikes think of five good things of your immediate condition
Re: Problem : can't find class
Hello,
try adding a "." to the classpath.
CLASSPATH=.:/usr/local/java/lib/classes.zip:/usr/local/java/jsdk/lib/jsdk.jar
Chris
Vinay Pai wrote:
>
> Hello,
>
> I am having the following problem when I try to execute a java program ,
> says :
> can't find class test
...
> The classpath variable is as follows :
>
> CLASSPATH=/usr/local/java/lib/classes.zip:/usr/local/java/jsdk/lib/jsdk.jar
>
> I am using Red Hat Linux 5.0 and jdk1.1.5.
--
public class chu extends ChrisHübsch implements TUChemnitz {
String email= "mailto:[EMAIL PROTECTED]";
String SMSMail = "mailto:[EMAIL PROTECTED]?Subject=SMS: info";
URL homepage = new URL("http://www.tu-chemnitz.de/~chu/");
Talktalkto = new Talk("[EMAIL PROTECTED]");
Integer ePlus= new Integer(4628555);
}
Re: Problem : can't find class
Common mistake. You need to have . (current directory) in your PATH. See the leading dot on the example below: CLASSPATH=.:/usr/local/java/lib/classes.zip:/usr/local/java/jsdk/lib/jsdk.jar Vinay Pai wrote: > > Hello, > > I am having the following problem when I try to execute a java program , > says : > can't find class test > This happens although the file test.class and test.java are in the same > directory from where I am executing java. I am however able to compile java > programs without any problems. Also I can run servlets through the browser. > The classpath variable is as follows : > > CLASSPATH=/usr/local/java/lib/classes.zip:/usr/local/java/jsdk/lib/jsdk.jar
Re: createImage() always returns null
Chris wrote: >is the Panel already visible? > >If not, then show() it before getting a Image! Or just do an addNotify() before...this gets the peers started
Automated C to Java conversion
I am looking for a Linux tool to generate Java source from C. I am aware of C2J/C2J++. What I need would have to be used repeatedly - the code will be maintained in C. Changing the C code once to match converters restrictions is feasible. Any recommendations? Commercial products included? b.
java programming
Hi all.
Does anyone know if one is allowed to initialize static final variables
within the "try" clause of a static initializer block?
(eg.
static final int x;
static{
try
{
x = 5;
}
catch(exception e)
{...and so on ..}
)
I am working on a software project which has code like this. I am
getting compile - time error messages which state that I am NOT allowed
to fo this. Are there some tricks one can use to "trick" the compiler.
I am assuming that the code previously worked(?). I am using
jdk1.1.5-glibc.
Any assistance would be high ly appreciated.
Thank YOU!
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Re: java programming
alexander lang writes:
> Does anyone know if one is allowed to initialize static final variables
> within the "try" clause of a static initializer block?
>
> (eg.
> static final int x;
> static{
> try
> {
> x = 5;
> }
> catch(exception e)
> {...and so on ..}
> )
>
> I am working on a software project which has code like this. I am
> getting compile - time error messages which state that I am NOT allowed
> to fo this. Are there some tricks one can use to "trick" the compiler.
> I am assuming that the code previously worked(?). I am using
> jdk1.1.5-glibc.
Final variables must be assigned along all possible execution paths of
the constructor or static initializer block. (Another way of saying
this is that there must not be a way to get through the constructor or
static initializer block without assigning to the final variable.)
Thus, if you assign to the final variable in the try section, you must
also assign it in the catch section.
I haven't looked in the spec to see what happens if a final variable
is assigned a value multiple times. I would imagine that its value is
the last value assigned. If this turns out to be a problem, you can
always do:
static final int x;
static {
int xx;
try {
xx = 5;
...
} catch (...) {
xx = 4;
}
x = xx;
}
Best,
daniel dulitz
Valley Technologies Peak Performance Real-Time DSP
State College, PA
Re: java programming
On Sun, 14 Feb 1999, alexander lang wrote:
> Hi all.
>
> Does anyone know if one is allowed to initialize static final variables
> within the "try" clause of a static initializer block?
>
> (eg.
> static final int x;
> static{
> try
> {
> x = 5;
> }
> catch(exception e)
> {...and so on ..}
> )
>
> I am working on a software project which has code like this. I am
> getting compile - time error messages which state that I am NOT allowed
> to fo this. Are there some tricks one can use to "trick" the compiler.
> I am assuming that the code previously worked(?). I am using
> jdk1.1.5-glibc.
>
> Any assistance would be high ly appreciated.
>
> Thank YOU!
>
> __
> Get Your Private, Free Email at http://www.hotmail.com
>
Hello,
I do not think that would be allowed. I just tried to compile this class
with the JDK 1.2 compiler and the jikes compiler and they do not accept it.
public class TryInStaticInit {
static final boolean cond;
static {
try
{
cond = true;
}
catch(Exception e) {
// do nothing
}
}
}
with javac from JDK 1.2
TryInStaticInit.java:3: Blank final variable 'cond' may not have been initialized. It
must be assigned a value in an initializer, or in every constructor.
static final boolean cond;
^
with jikes
Found 1 semantic error and issued 2 warnings compiling "TryInStaticInit.java":
3. static final boolean cond;
<-->
*** Error[116]: A blank class final variable must be initialized in a static
initializer block. It is assumed to be initialized
10. catch(Exception e) {
<->
*** Caution[ 186]: This catch block may be unreachable because there is no exception
whose type is assignable to "java/lang/Exception" that can be thrown during execution
of the body of the try block
I hope that helps
Mo DeJong
dejong at cs.umn.edu
simple imput from command line
Hope I'm not disturbing too much, probably I'm off topic but I'd need a simple way to imput a number (integer) from keyboard while a program is running in Java (JINI) I'd need a translation for basic : INPUT "AGE";A I'm able to do it from command line arg but not inside a program IF my question is too silly please ignore it. echo.java
Mailing List
I would like to be removed from your mailing list.
simple imput from command line
Hope I'm not disturbing too much, probably I'm off topic but I'd need a simple way to imput a number (integer) from keyboard while a program is running in Java (JINI) I'd need a translation for basic : INPUT "AGE";A I'm able to do it from command line arg but not inside a program IF my question is too silly please ignore it. echo (1).java
Re: simple imput from command line
cobra writes:
> IF my question is too silly please ignore it.
Well, you sent it twice. It's pretty silly, and it's off topic, but
now I'm worried that if everyone ignores it you'll keep sending it.
> I'd need a translation for basic : INPUT "AGE";A
import java.io.*;
public int getIntegerFromStandardInput ()
throws IOException, NumberFormatException {
final LineNumberReader lnr = new LineNumberReader
(new InputStreamReader (System.in), 1);
return (Integer.parseInt (lnr.readLine ()));
}
Please buy and read an introductory book on Java.
Best,
daniel dulitz
CLASSPATH variable too large ?
I have a large amount of .jar files in the library directory, and that leads to a very large CLASSPATH variable. The seems that java (java version "1.1.7") won't accept the classpath when it reaches a certain amount of characters. I currently have 331 characters in the path, and when I run a .class file java reports that the class can't be found. If I set the classpath to a much smaller amount of characters the program runs... Any suggestions on how to solve this problem (except from decompressing all the .jar files in the library directory) ? With regards, Ken A. Redergård http://www.colargol.tihlde.hist.no/~kenr
Re: CLASSPATH variable too large ?
On Mon, 15 Feb 1999, Ken A Redergard wrote: > I have a large amount of .jar files in the library directory, and that > leads to a very large CLASSPATH variable. > > The seems that java (java version "1.1.7") won't accept the > classpath when it reaches a certain amount of characters. I currently have > 331 characters in the path, and when I run a .class file java reports that > the class can't be found. If I set the classpath to a much smaller amount > of characters the program runs... > > Any suggestions on how to solve this problem (except from decompressing > all the .jar files in the library directory) ? > > With regards, > Ken A. Redergård > http://www.colargol.tihlde.hist.no/~kenr > You could try to use the -classpath argument to java. That should not be constrained by the max size for env vars. You would need a startup script otherwise you would have to type them all in every time you ran the java (yuk!). mo dejong dejong at cs.umn.edu
Re: Mailing List
> I would like to be taken off your mailing list.
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