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Unable to use package...why ???

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  Unable to use package...why ??? PortisHead <massivetdm850@gmail.com> - 2011-10-25 00:06 -0700
    Re: Unable to use package...why ??? Nigel Wade <nmw-news@ion.le.ac.uk> - 2011-10-25 10:32 +0100
      Re: Unable to use package...why ??? PortisHead <massivetdm850@gmail.com> - 2011-10-25 04:10 -0700
        Re: Unable to use package...why ??? Nigel Wade <nmw-news@ion.le.ac.uk> - 2011-10-25 13:07 +0100
          Re: Unable to use package...why ??? markspace <-@.> - 2011-10-25 07:47 -0700
            Re: Unable to use package...why ??? PortisHead <massivetdm850@gmail.com> - 2011-10-25 15:03 -0700
              Re: Unable to use package...why ??? PortisHead <massivetdm850@gmail.com> - 2011-10-25 15:10 -0700
                Re: Unable to use package...why ??? Martin Gregorie <martin@address-in-sig.invalid> - 2011-10-26 00:06 +0000
                  Re: Unable to use package...why ??? Martin Gregorie <martin@address-in-sig.invalid> - 2011-10-26 00:08 +0000
                Re: Unable to use package...why ??? Martin Gregorie <martin@address-in-sig.invalid> - 2011-10-26 00:06 +0000
            Re: Unable to use package...why ??? PortisHead <massivetdm850@gmail.com> - 2011-10-25 15:21 -0700
              Re: Unable to use package...why ??? markspace <-@.> - 2011-10-25 15:57 -0700
              Re: Unable to use package...why ??? Lew <lewbloch@gmail.com> - 2011-10-25 20:05 -0700
            Re: Unable to use package...why ??? Nigel Wade <nmw-news@ion.le.ac.uk> - 2011-10-26 09:55 +0100
              Re: Unable to use package...why ??? PortisHead <massivetdm850@gmail.com> - 2011-10-26 13:08 -0700
    Re: Unable to use package...why ??? Roedy Green <see_website@mindprod.com.invalid> - 2011-10-27 07:20 -0700
    Re: Unable to use package...why ??? Lew <lewbloch@gmail.com> - 2011-10-27 07:33 -0700
      Re: Unable to use package...why ??? PortisHead <massivetdm850@gmail.com> - 2011-10-28 12:57 -0700

#9165 — Unable to use package...why ???

Hello , I'm new to Java and tried the following.

First I created the file : Getbcard.java
inside the directory : C:\myclasses\exam\test\dok
below is the script :
package exam.test.dok;
public class Getbcard
{
public void setname()
{
System.out.println("Hello");
}
}

then , I compiled it using this command line:
javac Getbcard.java
and got the appropriated .class file:
Getbcard.class

Next , I created a new file , named : Showbcard.java in folder : C:
\examples
below is the script :
import exam.test.dok.*;
public class Showbcard
{
public static void main(String[] args)
{
System.out.println("Showbcard");
Getbcard i = new Getbcard();
i.setname();
}
}


then , I compiled it using this command line:
javac -cp c:\myclasses Showbcard.java
and got the appropriated .class file:
Showbcard.class

Now when I try to execute the file like :
java -cp c:\myclasses Showbcard

I get the error : Could not find or load main class Showbcard

What am I doing wrong here ?

Many , many thanks in advance

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#9167

On 25/10/11 08:06, PortisHead wrote:
> Hello , I'm new to Java and tried the following.
>
> First I created the file : Getbcard.java
> inside the directory : C:\myclasses\exam\test\dok
> below is the script :
> package exam.test.dok;
> public class Getbcard
> {
> public void setname()
> {
> System.out.println("Hello");
> }
> }
>
> then , I compiled it using this command line:
> javac Getbcard.java
> and got the appropriated .class file:
> Getbcard.class
>
> Next , I created a new file , named : Showbcard.java in folder : C:
> \examples
> below is the script :
> import exam.test.dok.*;
> public class Showbcard
> {
> public static void main(String[] args)
> {
> System.out.println("Showbcard");
> Getbcard i = new Getbcard();
> i.setname();
> }
> }
>
>
> then , I compiled it using this command line:
> javac -cp c:\myclasses Showbcard.java
> and got the appropriated .class file:
> Showbcard.class
>
> Now when I try to execute the file like :
> java -cp c:\myclasses Showbcard
>
> I get the error : Could not find or load main class Showbcard
>
> What am I doing wrong here ?
>
> Many , many thanks in advance

You only have the path to Getbcard in your classpath. You also need to 
add the path to Showbcard, so java knows where to locate it. From the 
limited code you've posted it looks as though Showbcard has no package, 
so adding "." (the current directory) to the classpath should suffice. 
Normally the default classpath will include ".", but by overriding it 
with the -cp argument you have removed ".".

I don't use the java command on Windows directly, so I'm not sure of the 
exact syntax of the -cp argument in Windows. In UNIX/Linux it's a colon 
separated list of paths, but in Windows-land the colon may interfere 
with the ":" as a drive letter separator. Check your local documentation 
for the java command, failing that Google should find the answer.

-- 
Nigel Wade

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#9171

Hi Nigel

When compiling the Showbcard.java file I included the path where the
package classes reside.
Thus :

javac -cp c:\myclasses Showbcard.java

(and it compiles without any errors , producing a Showbcard.class
file)

Also inside the Showbcard.java file , first line states : import
exam.test.dok.*;

Even when i try to execute it (with java command) , I provide exactly
the class-path,
thus :

 java -cp c:\myclasses Showbcard

???

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#9172

On 25/10/11 12:10, PortisHead wrote:
> Hi Nigel
>
> When compiling the Showbcard.java file I included the path where the
> package classes reside.
> Thus :
>
> javac -cp c:\myclasses Showbcard.java
>
> (and it compiles without any errors , producing a Showbcard.class
> file)
>
> Also inside the Showbcard.java file , first line states : import
> exam.test.dok.*;
>
> Even when i try to execute it (with java command) , I provide exactly
> the class-path,
> thus :
>
>   java -cp c:\myclasses Showbcard
>

That classpath only contains the location of the Getbcard class. It does 
not include the location of Showbcard. Hence java cannot locate the 
Showbcard.class file.

javac will look in the current directory for .java files, java will only 
do so if the current directory is in the classpath. Your classpath does 
not include the current directory (I'm assuming you are in the same 
directory as Showbcard.class). You need to include the path to 
Showbcard.class in the classpath.

-- 
Nigel Wade

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#9173

On 10/25/2011 5:07 AM, Nigel Wade wrote:
> On 25/10/11 12:10, PortisHead wrote:
>>
>> java -cp c:\myclasses Showbcard
>>
>
> That classpath only contains the location of the Getbcard class. It does
> not include the location of Showbcard. Hence java cannot locate the
> Showbcard.class file.



Specifically, you said you put Showbcard in \examples, not \myclasses.

   java -cp c:\myclasses;c:\examples Showbcard

I don't know how your previous claim that you compiled Showbcard with 
the class path of c:\myclasses worked.  I think there's a mistake in the 
sequence of events you showed us.

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#9179

The goal to achive is to make Showbcard use Getbcard via the "import"
command.
Thats why Showbcard is in a different directory.
If both classes where in the same directory , I didn't need to make
use of the "package" and "import" techniques.

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#9180

Sorry guys...
I tried what markspace told me...and it worked :)

Thus : java -cp c:\myclasses;c:\examples Showbcard
seems to made the difference.

Only thing that I don't understand is...why the above command needs
the "c:\examples" path to work properly ???

The "imported" class is in c:\myclasses , OK , but why does it need
also a reference to the current directory ???

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#9185

On Tue, 25 Oct 2011 15:10:43 -0700, PortisHead wrote:

> The "imported" class is in c:\myclasses , OK , but why does it need also
> a reference to the current directory ???
>
The imported class has two rather different uses:

1)the compiler reads it so it can check that what you wrote does actually
  match the constructors and classes you're trying to call, but that is 
  all it does with it. 'import' doesn't mean that the class is imported
  into your code. Instead it means that its symbol table is imported into
  the javac compiler.

2)the java command creates a JVM containing your class containing the 
  static void mail(String[]) method and then searches the classpath 
  to find *and load* the classes your source mentioned in import
  statements together with classes they imported and so on, in a cascade
  until all these references are satisfied. Then, and only then, can the
  program run. 

The loader is probably getting classes from a collection of jar files 
which are probably not in the same place in the filing system as they 
were when the code was compiled. Indeed, its quite likely that the 
imported class wasn't even in a jarfile at compile time. All that matters 
is that the packagename.ClassName is the same, relative to the runtime 
classpath, as the packagename.ClassName was relative to the classpath 
that was passed to the compiler. 

This is why the compiler class path needs to include "." if packagename 
is the name of the directory that contains ClassName.class relative to 
the directory where you ran the compiler BUT can still be found when 
packagename.ClassName.class has been packaged up in a jar file and put in 
some random directory and included in the runtime classpath.


-- 
martin@   | Martin Gregorie
gregorie. | Essex, UK
org       |

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#9187

On Wed, 26 Oct 2011 00:06:01 +0000, Martin Gregorie wrote:

> On Tue, 25 Oct 2011 15:10:43 -0700, PortisHead wrote:
> 
>> The "imported" class is in c:\myclasses , OK , but why does it need
>> also a reference to the current directory ???
>>
> The imported class has two rather different uses:
>
......

Apologies for the double post, but my line went down as I pressed the 
button and, after getting the link back online, I thought it hadn't been 
sent.
 

-- 
martin@   | Martin Gregorie
gregorie. | Essex, UK
org       |

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#9186

On Tue, 25 Oct 2011 15:10:43 -0700, PortisHead wrote:

> The "imported" class is in c:\myclasses , OK , but why does it need also
> a reference to the current directory ???
>
The imported class has two rather different uses:

1)the compiler reads it so it can check that what you wrote does actually
  match the constructors and classes you're trying to call, but that is 
  all it does with it. 'import' doesn't mean that the class is imported
  into your code. Instead it means that its symbol table is imported into
  the javac compiler.

2)the java command creates a JVM containing your class containing the 
  static void mail(String[]) method and then searches the classpath 
  to find *and load* the classes your source mentioned in import
  statements together with classes they imported and so on, in a cascade
  until all these references are satisfied. Then, and only then, can the
  program run. 

The loader is probably getting classes from a collection of jar files 
which are probably not in the same place in the filing system as they 
were when the code was compiled. Indeed, its quite likely that the 
imported class wasn't even in a jarfile at compile time. All that matters 
is that the packagename.ClassName is the same, relative to the runtime 
classpath, as the packagename.ClassName was relative to the classpath 
that was passed to the compiler. 

This is why the compiler class path needs to include "." if packagename 
is the name of the directory that contains ClassName.class relative to 
the directory where you ran the compiler BUT can still be found when 
packagename.ClassName.class has been packaged up in a jar file and put in 
some random directory and included in the runtime classpath.


-- 
martin@   | Martin Gregorie
gregorie. | Essex, UK
org       |

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#9181

On Oct 25, 5:47 pm, markspace <-@.> wrote:
> On 10/25/2011 5:07 AM, Nigel Wade wrote:
>
> > On 25/10/11 12:10, PortisHead wrote:
Sorry Guys.

I tried what markspace told me....and it worked :)

Thus :
java -cp c:\myclasses;c:\examples Showbcard

did the magic.
But I can't understand why , beside "C:\myclasses" where my class
files are stored , it needs the current path of Showbcard ???

Showbcard , imports Getbcard in its scripting.
So it makes pretty much good sense to include the "c:\myclasses" in
the -cp parameter of "java" command,
but why "C:\examples" ???

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#9182

On 10/25/2011 3:21 PM, PortisHead wrote:
>
> Showbcard , imports Getbcard in its scripting.
> So it makes pretty much good sense to include the "c:\myclasses"


I think this is the problem here.  "Import" doesn't really import 
anything.  It just tells the compiler that the class is in use.  It's 
the java command that does the importing.  It needs the directory of 
each and every class you use, and it needs the .class files, not the 
.java files.

Go look at the location of the .class files you are using, and I think 
it'll make sense.

You can actually see the java command load classes if you use the 
-verbose option.


   java -verbose -cp c:\myclasses;c:\examples Showbcard

<http://download.oracle.com/javase/7/docs/technotes/tools/windows/java.html>

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#9191

PortisHead wrote:
> I tried what markspace told me....and it worked :)
> 
> Thus :
> java -cp c:\myclasses;c:\examples Showbcard
> 
> did the magic.
> But I can't understand why , beside "C:\myclasses" where my class
> files are stored , it needs the current path of Showbcard ???

How many question marks does it take to indicate an interrogative?

> Showbcard , imports Getbcard in its scripting.

There is no "scripting" involved.  Java is not a scripting language.

> So it makes pretty much good sense to include the "c:\myclasses" in
> the -cp parameter of "java" command,
> but why "C:\examples" ???

The Java tutorials have a pretty good section on packages and the "import" directive (not command).

Java finds all classes by the classpath.  If the classpath does not include the current directory ("."), then the current directory is not searched.

-- 
Lew

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#9198

On 25/10/11 15:47, markspace wrote:
> On 10/25/2011 5:07 AM, Nigel Wade wrote:
>> On 25/10/11 12:10, PortisHead wrote:
>>>
>>> java -cp c:\myclasses Showbcard
>>>
>>
>> That classpath only contains the location of the Getbcard class. It does
>> not include the location of Showbcard. Hence java cannot locate the
>> Showbcard.class file.
>
>
>
> Specifically, you said you put Showbcard in \examples, not \myclasses.
>
> java -cp c:\myclasses;c:\examples Showbcard
>
> I don't know how your previous claim that you compiled Showbcard with
> the class path of c:\myclasses worked. I think there's a mistake in the
> sequence of events you showed us.
>
>

I think the compilation should work because javac locates source files 
by normal file paths. It doesn't use the classpath to locate the java 
source files, only the supporting class files. So if you specify the 
command (as in the OP):
  javac -cp c:\myclasses Showbcard.java

it will compile the Showbcard.java source file in the current directory 
(no path), and attempt to locate any required classes via the supplied 
classpath.

OTOH java only uses class files, and similarly locates them via the 
classpath. The supplied classpath in the OP does not include the current 
directory (as I've already stated twice) so Showbcard.class cannot be found.

-- 
Nigel Wade





-- 
Nigel Wade

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#9212

Many thanks to all of you.
I really appreciated your help.

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#9246

On Tue, 25 Oct 2011 00:06:16 -0700 (PDT), PortisHead
<massivetdm850@gmail.com> wrote, quoted or indirectly quoted someone
who said :

>java -cp c:\myclasses Showbcard

you have to specify the fully qualified name with package.

See http://mindprod.com/jgloss/package.html
http://mindprod.com/jgloss/javaexe.html

-- 
Roedy Green Canadian Mind Products
http://mindprod.com
It should not be considered an error when the user starts something
already started or stops something already stopped. This applies
to browsers, services, editors... It is inexcusable to 
punish the user by requiring some elaborate sequence to atone,
e.g. open the task editor, find and kill some processes.

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#9247

PortisHead wrote:
> First I created the file : Getbcard.java
> inside the directory : C:\myclasses\exam\test\dok
> below is the script :
> package exam.test.dok;

"myclasses" is the root of the classpath for this class.  Directories that match up with packages descend from such a root.

> public class Getbcard
> {
> public void setname()
> {
> System.out.println("Hello");
> }
> }
> 
> then , I compiled it using this command line:
> javac Getbcard.java

From what directory?  Where is your "exam/test/dok/" directory path?  ("exam\test\dok" in Windows.)

> and got the appropriated .class file:
> Getbcard.class

In what directory?

> Next , I created a new file , named : Showbcard.java in folder : C:
> \examples

That sounds like a class with no package.  Do not mix classes in packages with classes in the "no-package" (the default package, which isn't really a package).

<http://download.oracle.com/javase/tutorial/java/concepts/package.html>

Packages have to match with directories, in the normal filesystem approach.  If they do not, you are fubared.

> below is the script :

Not a script.

> import exam.test.dok.*;
> public class Showbcard
> {
> public static void main(String[] args)
> {
> System.out.println("Showbcard");
> Getbcard i = new Getbcard();
> i.setname();
> }
> }
> 
> 
> then , I compiled it using this command line:
> javac -cp c:\myclasses Showbcard.java
> and got the appropriated .class file:
> Showbcard.class

In what directory?

> Now when I try to execute the file like :
> java -cp c:\myclasses Showbcard
> 
> I get the error : Could not find or load main class Showbcard
> 
> What am I doing wrong here ?

As mentioned upthread, you left out the package in the class for the "java" command.

<http://download.oracle.com/javase/tutorial/java/package/index.html>
<http://download.oracle.com/javase/tutorial/java/package/managingfiles.html>

Note:  Do not use the CLASSPATH variable.  Stick with the "-jar" or "-cp" options to set classpath.

<http://download.oracle.com/javase/7/docs/technotes/tools/index.html>
<http://download.oracle.com/javase/7/docs/technotes/tools/windows/javac.html>
<http://download.oracle.com/javase/7/docs/technotes/tools/windows/java.html>

-- 
Lew

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#9283

On Oct 27, 5:33 pm, Lew <lewbl...@gmail.com> wrote:
> PortisHead wrote:
> > First I created the file : Getbcard.java
> > inside the directory : C:\myclasses\exam\test\dok
> > below is the script :
> > package exam.test.dok;
>
> "myclasses" is the root of the classpath for this class.  Directories that match up with packages descend from such a root.
>
> > public class Getbcard
> > {
> > public void setname()
> > {
> > System.out.println("Hello");
> > }
> > }
>
> > then , I compiled it using this command line:
> > javac Getbcard.java
>
> From what directory?  Where is your "exam/test/dok/" directory path?  ("exam\test\dok" in Windows.)

From the same directory.That is -----> C:\myclasses\exam\test\dok

>
> > and got the appropriated .class file:
> > Getbcard.class
>
> In what directory?

In the same as above --->C:\myclasses\exam\test\dok



> > Next , I created a new file , named : Showbcard.java in folder : C:
> > \examples
>
> That sounds like a class with no package.  Do not mix classes in packages with classes in the "no-package" (the default package, which isn't really a package).
>
> <http://download.oracle.com/javase/tutorial/java/concepts/package.html>
>
> Packages have to match with directories, in the normal filesystem approach.  If they do not, you are fubared.
>
> > below is the script :
>
> Not a script.
>
>
>
>
>
>
>
>
>
> > import exam.test.dok.*;
> > public class Showbcard
> > {
> > public static void main(String[] args)
> > {
> > System.out.println("Showbcard");
> > Getbcard i = new Getbcard();
> > i.setname();
> > }
> > }
>
> > then , I compiled it using this command line:
> > javac -cp c:\myclasses Showbcard.java
> > and got the appropriated .class file:
> > Showbcard.class
>
> In what directory?

the Directory was ----> C:\examples


>
> > Now when I try to execute the file like :
> > java -cp c:\myclasses Showbcard
>
> > I get the error : Could not find or load main class Showbcard
>
> > What am I doing wrong here ?
>
> As mentioned upthread, you left out the package in the class for the "java" command.
>
> <http://download.oracle.com/javase/tutorial/java/package/index.html>
> <http://download.oracle.com/javase/tutorial/java/package/managingfiles...>
>
> Note:  Do not use the CLASSPATH variable.  Stick with the "-jar" or "-cp" options to set classpath.
>
> <http://download.oracle.com/javase/7/docs/technotes/tools/index.html>
> <http://download.oracle.com/javase/7/docs/technotes/tools/windows/java...>
> <http://download.oracle.com/javase/7/docs/technotes/tools/windows/java...>
>
> --
> Lew

Thanks again Lew for all the suggestions !!!

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