I have written a simple hello world program given below
package helloworld;
public class helloWorld
{
public static void main(String[] args)
{
System.out.println("Hello, World!");
}
}
I'm using Windows 7 and have set my CLASSPATH and PATH variables in the environment variables window as
C:\Program Files\Java\jdk1.6.0_24\bin;
The program is located at
C:\Users\Admin\Documents\NetBeansProjects\javaAssignment\src\helloWorld
So, basically when i try to run it in my command prompt, the following happens
C:\Users\Admin\Documents\NetBeansProjects\javaAssignment\src\helloWorld>javachelloWorld.java
C:\Users\Admin\Documents\NetBeansProjects\javaAssignment\src\helloWorld>java helloWorld
Exception in thread "main" java.lang.NoClassDefFoundError: helloWorld (wrong name: helloworld/helloWorld)
at java.lang.ClassLoader.defineClass1(Native Method)
at java.lang.ClassLoader.defineClassCond(ClassLoader.java:632)
at java.lang.ClassLoader.defineClass(ClassLoader.java:616)
at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:141)
at java.net.URLClassLoader.defineClass(URLClassLoader.java:283)
at java.net.URLClassLoader.access$000(URLClassLoader.java:58)
at java.net.URLClassLoader$1.run(URLClassLoader.java:197)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:190)
at java.lang.ClassLoader.loadClass(ClassLoader.java:307)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301)
at java.lang.ClassLoader.loadClass(ClassLoader.java:248)
Could not find the main class: helloWorld. Program will exit.
The program seems to be compiling fine and does not throw any errors. But when i try to run it, it says than exceptions have occurred.
I tried looking up on Google thinking that setting my PATH and CLASSPATH was wrong, but I don't seem to find any issues with that.
In case your helloWorld.java file is in a package, you can run as follows :
C:\Users\Admin\Documents\NetBeansProjects\javaAssignment\src\
java packageName.helloWorld
Run the code from outside the helloworld package directory i.e from src directory (C:\Users\Admin\Documents\NetBeansProjects\javaAssignment\src)
Also check if the name of your java file is the same as your class name (helloWorld.java)
Also it seems that the name of your package is helloworld (all in small letters) however the folder name is helloWorld (note that W is capital) both the names need to match.
You need to make sure you are in the directory containing your helloWorld.class file when you issue the command
java helloWorld
Related
This question already has answers here:
NoClassDefFoundError: wrong name
(8 answers)
Closed 9 years ago.
I'm just trying to compile a simple hello world file via the terminal.
Here's the code for Hello.java:
package Hello;
public class Hello {
public static void main(String[] args) {
System.out.println("Hello, world!");
}
}
this is saved in another folder, so in terminal I typed:
cd code/repositories/java to navigate to the correct directory (where I saved Hello.java)
I next typed javac Hello.java and hit return. It compiled without any errors.
I then tried to open the file with java Hello and it threw the following exception:
Exception in thread "main" java.lang.NoClassDefFoundError: Hello (wrong name: Hello/Hello)
at java.lang.ClassLoader.defineClass1(Native Method)
at java.lang.ClassLoader.defineClassCond(ClassLoader.java:631)
at java.lang.ClassLoader.defineClass(ClassLoader.java:615)
at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:141)
at java.net.URLClassLoader.defineClass(URLClassLoader.java:283)
at java.net.URLClassLoader.access$000(URLClassLoader.java:58)
at java.net.URLClassLoader$1.run(URLClassLoader.java:197)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:190)
at java.lang.ClassLoader.loadClass(ClassLoader.java:306)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301)
at java.lang.ClassLoader.loadClass(ClassLoader.java:247
How/why does this happen and how do I go about fixing it?
The package is called Hello which makes the full qualified name Hello.Hello which means you need to have your Hello.java file in code/repositories/java/Hello
then cd to the code/repositories/java folder and call javac javac Hello/Hello.java then you can run it java Hello.Hello
On a different note, Java standard naming conventions recommend package names use lowercase letters so consider changing the package to "hello"
Remove line package Hello;. Compile and run.
So I'm trying to compile and run a problem in java and I can't get it to run. I'm just trying to do a basic package with a HelloWorld class and a main function that prints "hello world."
package helloworld;
public class HelloWorld {
public static void main(String args[]) {
System.out.println("Hello world \n");
}
}
then I call javac HelloWorld.java to compile it. Then when I try to execute the code I get this error:
Exception in thread "main" java.lang.NoClassDefFoundError: HelloWorld (wrong name: helloworld/HelloWorld)
at java.lang.ClassLoader.defineClass1(Native Method)
at java.lang.ClassLoader.defineClassCond(ClassLoader.java:631)
at java.lang.ClassLoader.defineClass(ClassLoader.java:615)
at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:141)
at java.net.URLClassLoader.defineClass(URLClassLoader.java:283)
at java.net.URLClassLoader.access$000(URLClassLoader.java:58)
at java.net.URLClassLoader$1.run(URLClassLoader.java:197)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:190)
at java.lang.ClassLoader.loadClass(ClassLoader.java:306)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301)
at java.lang.ClassLoader.loadClass(ClassLoader.java:247)
Edit:
I am trying to run the code using the command "java HelloWorld"
Lets see if you understand what I did
tmp$ mkdir helloworld
tmp$ vi helloworld/HelloWorld.java
#paste the content of the class *including* package definition
tmp$ cd helloworld/
helloworld$ javac HelloWorld.java
helloworld$ java HelloWorld
Exception in thread "main" java.lang.NoClassDefFoundError: HelloWorld (wrong name: helloworld/HelloWorld)
at java.lang.ClassLoader.defineClass1(Native Method)
at java.lang.ClassLoader.defineClassCond(ClassLoader.java:631)
at java.lang.ClassLoader.defineClass(ClassLoader.java:615)
at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:141)
at java.net.URLClassLoader.defineClass(URLClassLoader.java:283)
at java.net.URLClassLoader.access$000(URLClassLoader.java:58)
at java.net.URLClassLoader$1.run(URLClassLoader.java:197)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:190)
at java.lang.ClassLoader.loadClass(ClassLoader.java:306)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301)
at java.lang.ClassLoader.loadClass(ClassLoader.java:247)
Could not find the main class: HelloWorld. Program will exit.
helloworld$ cd ..
tmp$ java helloworld.HelloWorld
Hello world
Also, read this: http://www.cs.usfca.edu/~parrt/course/601/lectures/java.tools.html
Perform the following steps
1. Copy the HelloWorld.java file to a empty directory
2. javac -d . HelloWorld.java
3. java -classpath . helloworld.HelloWorld
There were 2 problems with your setup.
1. you need to use -d option while compiling. This will generate .class files according to the package structure. This is useful for running the .class file. This is so because java expects .class files in package structure.
2. specify the classpath as '.' which stands for current directory to run the program.
you can also use this
1. javac -d c:\temp HelloWorld.java
3. java -classpath c:\temp helloworld.HelloWorld
just change your classname from Helloworld to any other(like hl) and run like this (assume in e drive)
E:>cd helloworld
E:\helloworld>javac hl.java
E:\helloworld>cd ..
E:>java helloworld.hl
Hello world
This program compiles and runs swimmingly in eclipse on the same machine, but I'd really like to work from the command line and my editor of choice.
CollectNewspaperKarel.java
import stanford.karel.*;
public class CollectNewspaperKarel extends SuperKarel {
public void run() {
// You fill in this part
}
}
The karel.jar is in the same directory as the file above.
Compile
javac -cp karel.jar CollectNewspaperKarel.java
with no errors.
Run
java -cp karel.jar CollectNewspaperKarel
Exception in thread "main" java.lang.NoClassDefFoundError: CollectNewspaperKarel
Caused by: java.lang.ClassNotFoundException: CollectNewspaperKarel
at java.net.URLClassLoader$1.run(URLClassLoader.java:202)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:190)
at java.lang.ClassLoader.loadClass(ClassLoader.java:306)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301)
at java.lang.ClassLoader.loadClass(ClassLoader.java:247)
you forgot to include your class to classpath when running the program.
Try this - if running on windows:
java -cp karel.jar;CollectNewspaperKarel.class CollectNewspaperKarel
or this if you're running on linux:
java -cp karel.jar:CollectNewspaperKarel.class CollectNewspaperKarel
One more thing however, you need to have main method in your class, otherwise it won't work :)
Update:
I've found following site: http://ycsoftware.net/setting-up-karel-the-robot-in-eclipse/
seems, you should go with the following arguments if you have the same version of karel as the author there:
on windows:
java -cp karel.jar;CollectNewspaperKarel.class stanford.karel.Karel code=CollectNewspaperKarel
on linux:
java -cp karel.jar:CollectNewspaperKarel.class stanford.karel.Karel code=CollectNewspaperKarel
Peter B. is right, however you cannot run a class containing a "run" method alone, you need a public static void(String[] args) method to make it runnable.
I suppose that in Eclipse some other class is used as a "main class" to run the thing.
$cat JarTest.java
package edu.testjava.simple;
public class JarTest
{
public static void main(String args[])
{
System.out.println("Hello World\n");
}
}
$javac JarTest.java
$java JarTest
I get error:
Exception in thread "main" java.lang.NoClassDefFoundError: JarTest (wrong name: edu/testjava/simple/JarTest)
at java.lang.ClassLoader.defineClass1(Native Method)
at java.lang.ClassLoader.defineClassCond(ClassLoader.java:632)
at java.lang.ClassLoader.defineClass(ClassLoader.java:616)
at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:141)
at java.net.URLClassLoader.defineClass(URLClassLoader.java:283)
at java.net.URLClassLoader.access$000(URLClassLoader.java:58)
at java.net.URLClassLoader$1.run(URLClassLoader.java:197)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:190)
at java.lang.ClassLoader.loadClass(ClassLoader.java:307)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301)
at java.lang.ClassLoader.loadClass(ClassLoader.java:248)
Could not find the main class: JarTest. Program will exit.
Why so?
Anything wrong with package etc?
Thanks!
You need to do:
$ java -cp . edu.testjava.simple.JarTest
You need to specify the name of the class with the full package name (in this case edu.testjava.simple). You don't need .class or .java on the end.
You can also see the answers to How to execute a java .class from the command line.
Yes, it's because of the package. Java enforces the project structure to be the same as the package structure. That means, that the class in the edu.testjava.simple package must be located in the edu/testjava/simple/ directory.
You may either:
Remove package declaration (this, however, is only acceptable in such "hello world" cases)
Compile the file using javac -d . JarTest.java (this will put the .class file in the appropriate directory) and launch it via java edu.testjava.simple.JarTest
I created a file called "Hello.java" that looks like this:
public class Hello {
public static void main(String[] args) {
System.out.println("Hello, world!");
}
}
I ran javac Hello.java, then java Hello, and everything worked as expected.
I then added the line package testpackage; to the top of the file, and put it in the directory /home/matthew/Desktop/hellotest/testpackage. I put .:/home/matthew/Desktop/hellotest in my CLASSPATH, and compiled and ran the same way as before. But now, I get this error:
matthew#matthew-laptop:~/Desktop/hellotest/testpackage$ java Hello
Exception in thread "main" java.lang.NoClassDefFoundError: Hello (wrong name: testpackage/Hello)
at java.lang.ClassLoader.defineClass1(Native Method)
at java.lang.ClassLoader.defineClass(ClassLoader.java:634)
at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:142)
at java.net.URLClassLoader.defineClass(URLClassLoader.java:277)
at java.net.URLClassLoader.access$000(URLClassLoader.java:73)
at java.net.URLClassLoader$1.run(URLClassLoader.java:212)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:205)
at java.lang.ClassLoader.loadClass(ClassLoader.java:321)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:294)
at java.lang.ClassLoader.loadClass(ClassLoader.java:266)
at java.lang.ClassLoader.loadClassInternal(ClassLoader.java:334)
Could not find the main class: Hello. Program will exit.
Why did it work on its own, but not in a package?
Now that it's in testpackage, its name is really testpackage.Hello. So go up a directory and do java on that.
Go up one directory, and run:
java testpackage.Hello
Try java testpackage.Hello.
Because this is in your classpath, you should be able to run that from any working directory, but refer to it by its full name.