Java Class.java doesn't work??

I've compiled my java file with javac. But then when I type: java ClassName : for example it gives me exception in thread "main" java.lang.NoClassFoundDefError:
I've already set the path, so I don't think that's the problem. Help please. Thanks in advance.

I got the problem all the sudden - it was ok before. even after I reinstalled jdk1.3 as well as jdk1.4, I still got the same error message. I've gotten all the java_home, Path and Classpath setup (worked for a quite long time). I was testing JNDI when I noticed that problem - before that I was testing J2ee stuff and it seems works fine...
any comment?
(error: java.lang.noClassDefFoundError)
thanks.

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Sort(java.util.LinkedList java.lang.Object ) doesn't work

Why doesn't this work?
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Collections.sort(sysPropsKeys);
cannot fnd symbol
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location: class java.util.Collections

I will admit to not having Java1.5 installed on my machine. Haven't yet had the chance to play with generics, but the above DOES work in 1.4, and SHOULD work in 1.5
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AFAIK string are comparable, and shouldn't throw class cast exceptions
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Ok, I can see your point in that some hackers abuse the Properties class by putting non string keys/values into the Properties Map. In that case the code would become more like your above. I'd probably still go with a TreeMap though, rather than a sorted list of keys. Most time you want the keys, you want the values as well. So if the intention is to print out a sorted list of system properties, and their values, keeping it in a map is best.
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Class unloading doesn't work as described in this forum !!!

Hi,
to the problem of dynamic class unloading many people in this forum wrote:
- write your own class loader
- load the class to be unloaded later
- set all instances of your own class loader to null
- if the work is done set all instances of the loaded classes to null
- call the garbage collector and the classes will be removed
I constructed a simple test for the problem:
- the test class
public class Impl {
public String getVersion () {
return "1";
- instanciating the test class
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- instanciating the test class
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the parent of it. If no parameter is given to a class loader's constructor the parent of a class loader
is the system classloader.
Let's have a look at the source code of java.lang.ClassLoader.loadClass(...):
protected synchronized Class loadClass(String name, boolean resolve)
throws ClassNotFoundException
// First, check if the class has already been loaded
Class c = findLoadedClass(name);
if (c == null) {
try {
if (parent != null) {
### here the loadClass() of the parent is called and the
### loaded class is stored within the parent
c = parent.loadClass(name, false);
} else {
c = findBootstrapClass(name);
} catch (ClassNotFoundException e) {
// If still not found, then call findClass in order
// to find the class.
c = findClass(name);
if (resolve) {
resolveClass(c);
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My Idea was: Give a null to the class loader's constructor so the classes cannot be stored within a parent.
Here my test class loader (it is build as it is described within javadoc of java.lang.ClassLoader
except the constructor):
import java.io.*;
public class MyClassLoader extends ClassLoader {
public MyClassLoader () {
super ( null );
public Class findClass ( String name ) {
byte[] b = loadClassData ( name );
return defineClass ( name, b, 0, b.length );
private byte[] loadClassData ( String name ) {
byte[] ret = null;
try {
InputStream in = new FileInputStream ( name + ".class" );
ret = new byte[in.available ()];
in.read ( ret );
} catch ( Exception e ) {
e.printStackTrace ();
return ret;
The loading of the class works fine
ClassLoader cl = new MyClassLoader ();
Class c = cl.loadClass ( "Impl" );
Object i = c.newInstance ();
Impl impl = (Impl)i;
The class "Impl" was found and instanciated. But the cast "Impl impl = (Impl)i;" causes a
"java.lang.ClassCastException: Impl"
May second idea was deleting all instances of the class to unload from the class loader via reflection.
A strange way I know but if this is the only way I will do it. But this doesn't work too.
After deleting the class from the class loader and all its parents the class is still anywhere in the depth
of the VM.
Can anybody help me with this problem?
Thanks in advance,
Axel.

<pre>
I made a similar and simpler program and it worked:
import java.net.URLClassLoader;
import java.net.URL;
public class DynamicExtension {
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C:\Java\TIJ2\Test>java DynamicExtension
version 1
version 2
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finalizing LoadableObject@4abc9
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In the source code for ClassLoader
there is the following:
* The classes loaded by this class loader. The only purpose of this
* table is to keep the classes from being GC'ed until the loader
* is GC'ed.
private Vector classes = new Vector(); /*
and:
* Called by the VM to record every loaded class with this loader.
void addClass(Class c) {
classes.addElement(c);
I would like to have seen findLoadedClass checking the already loaded classes in this Vector, but this method is native. Anyway, as the code for loadClass shows, the parent or bootstrap classloader is checked if findLoadedClass doesn?t find the class; Can we guess that findLoadedClass only checks the clases loaded by the classloader, not its parent?
By the way, could an example like this be made in c++?
</pre>

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Hi,
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import java.io.*;
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import swarm.sys.interfaces.*;
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Hi,
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[http://support.mozilla.com/en-US/kb/Uninstalling+add-ons Uninstalling Add-ons]
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Hello all:
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However, I think the correct output should be:
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====================================
<pre>
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Hi,
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Yes, you need to have the Java source, with the -sourcepath option, as described here:
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Hi there:
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Hi there:
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Hi all,
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Just to understand: is File2 ar jar archive or not? If it is a jar archive, have you tried open File2.jar? If File2 is a directory within the current directory, have you tried java -cp . File2/File? I just tested with a set of classes and it works... Let me be precise:
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Java Class.java doesn't work??

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