How to use class.forName

I am trying to use Class.forName() from a string which is passed to me as argument.
Class batchClass = Class.forName(args[1]);
A jar file contains the class file for the string received above and I have this jar file in the manifest of my executable jar.
I get a class not found exception when I run my executable jar
Can some body give pointers..what could possibly be the issue.
The jar file is in my classpath
run script
#!/bin/csh
java -jar -DDBPROVIDER=NO -DDBUS_ROOT=$DBUS_ROOT -DVTNAME=$VTNAME ./jar/IntraDayDepotPositionBatch.jar MagellanStart IntraDayDepotPositionBatch INPUTFILE LOGFILE
Exception
Magellan program starting - program class IntraDayDepotPositionBatch
Cannot find program class - IntraDayDepotPositionBatch
IntraDayDepotPositionBatch
java.lang.ClassNotFoundException: IntraDayDepotPositionBatch
at java.net.URLClassLoader$1.run(URLClassLoader.java:200)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:188)
at java.lang.ClassLoader.loadClass(ClassLoader.java:306)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:268)
at java.lang.ClassLoader.loadClass(ClassLoader.java:251)
at java.lang.ClassLoader.loadClassInternal(ClassLoader.java:319)
at java.lang.Class.forName0(Native Method)
at java.lang.Class.forName(Class.java:164)
at com.db.mmrepo.app.IntraDayDepotPositionBatch.MagellanStart.main(Unknown Source)
Thanks for your time and feedback on this

actually i tried both...with package name and without package name..
nothing worked...
my manifest file also contains the path to the package..so does the classpath

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How to create an object of our own class by using Class.forName()??

how to create an object of our own class by using Class.forName()??
plzz anser my qustion soon..

Class.forName does not create an object. It returns a reference to the Class object that describes the metadata for the class in question--what methods and fields it has, etc.
To create an object--regardless of whether it's your class or some other class--you could call newInstance on the Class object returned from Class.forName, BUT only if that class has a no-arg constructor that you want to call.
Class<MyClass> clazz = Class.forName("com.mycompany.MyClass");
MyClass mine = clazz.newInstance();If you want to use a constructor that takes parameters, you'll have to use java.lang.reflect.Constructor.
Google for java reflection tutorial for more details.
BUT reflection is often abused, and often employe when not needed. Why is it that you think you need this?

ClassNotFoundException when using Class.forName(), thx

in a study app, i try to use Class.forName() to load any class then get its properties (fields, methods etc. vs reflect).
the (Frame based) app is in directory:
c:\app\StudyApp.class
there is a "Open class" button on the app, click the button, i use FileChooser to open any class file.
i.e. open a class (assume it is not packaged)
d:\dir\TheClass.class
coding in StudyApp.java is:
Class cls=Class.forName("TheClass");
now a ClassNotFoundException throws when call Class.forName() above.
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d:\dir
my question is: how to tell VM the directory.
the directory d:\dir can not be applied to -classpath when run java.exe StudyApp, because the directory is random one at run-time.
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This probably does a lot more than you need:
import java.util.*;
import java.io.*;
import java.util.jar.*;
import java.lang.*;
public class ClassFileFinder extends ClassLoader
     List cpath = new LinkedList();
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          String cname = className.replace('.', File.separatorChar) + ".class";
          Iterator it = cpath.iterator();
          while(it.hasNext()) {
               File f = (File)it.next();
               try {
                    if(f.isDirectory()) {
                         File cFile = new File(f, cname);
                         if(cFile.isFile()) {
                              byte[] buf = new byte[(int)cFile.length()];
                              InputStream in = new FileInputStream(cFile);
                              int off = 0, l;
                              while((l = in.read(buf, off, buf.length - off)) > 0) {
                                   off += l;
                                   if(off >= buf.length) break;
                              in.read(buf);
                              in.close();
                              return buf;
                    } else if (f.isFile()) {
                         JarFile jar = new JarFile(f);
                         JarEntry ent = jar.getJarEntry(cname);
                         if(ent != null) {
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                              int off = 0, l;
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                              while((l = in.read(buf, off, buf.length - off)) > 0) {
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                                   if(off >= buf.length) break;
                              in.close();
                              return buf;
               } catch (IOException e) {
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     public Class findClass(String className) throws ClassNotFoundException{
          byte[] data = classData(className);
          if(data == null)
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               return defineClass(className,data,0, data.length);
}Create an instance, Add directories and/or jar files with addFile then loadClass the class you want.

Database connectivity without using Class.forName()

Hi,
Can anyone please tell how we can connect to a database without in java without using the Class.forName() method , and then how the database driver gets loaded.
Regards,
Tanmoy

Hi,
I recently wrote code that connects to a database without using Class.forName() in order to be compatible with Microsoft's JVM. I read about it here:
http://www.idssoftware.com/faq-e.html#E1
Basically, you create a new Driver object and use its connect method.
Here's what my particular code ended up being:
String url = "jdbc:mysql://localhost:3306/test?user=root&password=mypass";
Driver drv = new org.gjt.mm.mysql.Driver();
Connection con = drv.connect(url,null);

Why use Class.forName() ?

Why is it always adviced to use Class.forName( nameOfTheDriver ). Why dont we simply import the driver via the import statement ?
Please note that this topic is part of a bigger topic I published in Java programming about difficulties I had importing driver. See:
http://forums.java.sun.com/thread.jsp?forum=31&thread=147534
for more details.

Because using an import statement only tells the compiler about the driver. Class.forName() actually loads the driver when the program runs, which is what you want to happen.

Need samples how to use classes in WebDynpro

Hi,
I Need To simple Samples how to use classes in WebDynpro.
Regards

Continued....
and in the model
right click->create model
select the radio button import java bean .
next ADD jars option will be seen
Browse the jar on the dekstop.
now add this model to the used models by right clicking on it.
Now if you go to Data Modeler.
You will find the used model.
From there map to the component controller->view Controller.
And continue with ur coding.
Hope this helps you.
Thanks & Regards,
Lokesh.

Why can't i use class.forName(str) ?

Heys all i have this piece of code which is working fine:
*try {*
java.lang.Class.forName("sun.jdbc.odbc.JdbcOdbcDriver");
*} catch (java.lang.ClassNotFoundException e) {*
now the problem is that i was under the impression that i could use class.forName("sun.jdbc.odbc.JdbcOdbcDriver"); but it wouldn't compile. does anyone know why is this so?

Class.forName() says "call the static method forName() that is defined in java.lang.Class". It returns a reference to an instance of java.lang.Class.
SomeClass.class is known as a class literal. It is not a member, not a field, not a method. It evaluates to a reference to an instance of java.lang.Class.
You cannot do class.something().
Edited by: jverd on Oct 26, 2010 9:46 AM

Instantiating object using Class.forName()

What is the difference between instantiating using Class.forName() method and instantiating using the new operator?

The difference is that you can use the new operator to instantiate an object, but you can't do it using Class.forName().
But seriously folks...
Presumably you're talking about Class.newInstance()--which often appears right on the heels of Class.forName().
New gives you compile-time checks you don't get with Class.forName(). If it compiles with new, then you know the constructor in question exists on the class in question.
With Class.newInstance() (and it's cousin (also called newInstance, I think) in the Constructor class), you can't be sure until you actually execute it whether that constructor even exists.
New requires you to know the class at compile time. NewInstance lets you defer the specific class until runtime.
New is simpler and more direct.
(Did I just do your homwork for you? Hope not.)

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Basically, I want to make
sure that when I null out the class loader, that the
class is removed from memory.The class is removed from memory when it is garbage, i.e. when there are no references to it left.
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- The classloader that loaded the class holds a reference to the class object.
Load a plugin which adds a menu item. Attempt
to unload the class (via nulling the class loader),
and clicking on the menu item.Obviously the class can't be unloaded while the menu item has a reference to an object of the class.
Also, one thing I
am confused on. It seems no matter what I use for the
URL object (in the try..catch block when creating it),
it always finds my plugins with the path attribute I
pass in.This obviously means that the bootstrap classloader finds your class. Remove the class from your classpath e.g. by moving it to a subdirectory.
Here is some sample code that should work. This is meant as a proof of concept, you probably want to do some things differently. I'm also writing this from the top of my head, so I can't guarantee that there are no errors here.//this file (Plugin.java) should be in your classpath
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If we change it back to the way it was we notice that when the MainClass class is loaded then only the Plugin (interface) class is loaded. This way the MyPlugin class won't be loaded until we load it manually through our own classloader, and this is exactly what we want.
This is why we usually handle all dynamically reloadable classes through interfaces instead of using the classes directly.
- Marcus

Need Help Loading Sqlbase Driver Using Class.forName(...

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bad class file: C:\com\centurasoft\java\sqlbase\SqlbaseDriver.class
class file contains wrong class: com.centurasoft.java.sqlbase.SqlbaseDriver
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// Create the ...
public class SqlbaseEx {
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"SUP_ID int, " +
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con.close();
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Thanks for the reply.
Upon further testing, I think my original post was slightly incorrect: if I use either of the following lines --
Class.forName("com.centurasoft.java.sqlbase.SqlbaseDriver");
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Class.forName("centura.java.sqlbase.SqlbaseDriver");
I get the following error at runtime:
ClassNotFoundException: com.centurasoft.java.sqlbase.SqlbaseDriver
or
ClassNotFoundException: centura.java.sqlbase.SqlbaseDriver
It is when I use the line -- Class.forName("SqlbaseDriver");
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Before I posted on JavaRanch, I put the Images folder at every level of the project's
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Hello guys!
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Your problem/question is not clear to me. If you are getting errors you should include the error messages in your posting.
Could the problem arise from using a variable that is not defined?
currentroom = "playroom";
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