With reference to this post
Receiving "wrong name" NoClassDefFoundError when executing a Java program from the command-line
I did not understand how to solve the problem
Actually in my java source code there' s line :
package es_2011;
when I compile the program through JCreator everything works perfectly.
It creates a folder named es_2011 where to put .class files.
Also the executing operation goes smoothly, the program runs ok.
Now I'd like to use the command line only.
So I placed my java file in the directory where javac.exe is but whenever I try to compile I get the same error
The command I use is: javac ProgAudioJ.java
The path (where javac.exe is ) is : C:\Program files\Java\jdk1.6.0_22\bin
Is someone willing to help me understand in terms of exactly tell me what I have to do?
thanks very much...MAX
The setup used for the looks like this (under windows)
C:\classDir -> is the project
C:\classDir\testpackage -> is the only package used (the package "testpackage")
C:\classDir\testpackage\Main.class -> is the class with the main method inside (important: it is the .class and not .java)
The Main.class looks like following:
package testpackage;
public class Main {
public static void main(String[] args) {
System.out.println("Program started! ;-)");
}
}
go with your command prompt to:
c:\classDir> java testpackage.Main
the result:
Program started! ;-)
According to your problems that it starts in your IDE but not from the console:
- checked if you realy use the path to the .class files?
- with the console go to the directory of you .class files, not the project (e.g. in Eclipse it is the bin directory
- enter the full qualified class name (including packages seperated by . -> e.g. testpackage.Main
More infos can be found under:
http://www.oracle.com/technetwork/java/compile-136656.html
Hope it helped
MAX, if the class defines that it's inside the package es_2011, then it should be in a folder with the same name.
So in your case, put the ProgAudioJ.java in the folder es_2011 and then run
javac es_2011\ProgAudioJ.java
latter to run it, you need the command
java es_2011.ProgAudioJ
You should add javac.exe in your path .Edit your path variable and append path to jdk's bin
then put java file in a dir named es_2011 , as the package declaration is es_2011 then compile
c:\es_2011\javac YourJava.java
and now go back to C:
c:\java es_2001.Yourjava
After reading you other Post: "Receiving "wrong name" NoClassDefFoundError when executing a Java program from the command-line" I guess you go to the directory es_2011 where your ProgAudioJ.class file is located and run
java ProgAudioJ
from that folder.
instaend you have to go to the folder above (cd ..) and run
java es_2011.ProgAudioJ
Each package in Java corresponds to a folder on the filesystem. So a package declaration such as com.stackoverflow would mean that the source classes need to be in a folder ./com/stackoverflow. Typically the whole project would have a separate src folder containing com/stackoverflow.
When you compile the Java classes you DO NOT need to put source files in the same directory as javac.exe, you do however need to make sure that javac.exe is in your operating systems PATH variable. This tells the operating system where it should look for executable files when a command is run, on a *nix machine this would usually be /usr/bin or just /bin but on Windows machine the executables normally live within the applications own directories, that is C:\Program Files\something. Assuming that you've installed JDK correctly, the javac.exe should already be in the PATH you can check this by opening the command line and just running javac (just like that). If you get some output then all is well, the system knows where to find javac.exe.
Next you will need to go to your project folder and type javac -d . src/com/stackoverflow/MainSO.java notice that is run from the project folder. This will create a folder called com in your project root and put the compiled classes in com/stackoverflow. The -d flag tells javac where to put the compiled classes, if you leave that out, the compiled classes will be where the sources are.
Then when you want to run the classes you type java com.stackoverflow.MainSO (no .class). Crucially this command will need to be ran in the directory that contains the root of the class hierarchy (that is the com folder containing the compiled classes). You can specify other places for java to look for the classes by providing a classpath to the java command with the -cp flag. By default the classpath will contain the directory the java command was ran in. Should your project have dependencies external .jar files for example you will need to provide every single one of them (with their full filepath) in the classpath (this goes for the compiler as well). The IDEs do this automatically for you.
Hope that helps.
Related
I'm on Ubuntu 22.04 trying to run my code in the terminal.
The program works without problems in VScode, also when running multiple instances.
The program is consisted of six class files.
The trouble occurs when I try and run it with terminal. When compiling the java file
with javac it shows errors at places where I use the external libraries.
If I compile it with VScode and run the class file in terminal, I get the following error java.lang.ClassNotFoundException
This is causing me problems since I'm also supposed to dockerize the program.
You can add the following code in your setting.json file "java.project.outputPath": "bin",
This will be the .class file generated by VS Code in the bin folder of the same directory when running the Java code.
You can use the java command after entering the file directory with the cd command.
This generally indicates that the class path with which you're compiling your program does not include the correct paths to your libraries. Assuming your libraries are jar files, your javac command should look something like this:
javac -cp libs/lib1.jar:libs/lib2.jar srcs/*.java
where libs/ is the relative path to your libraries and srcs/ is the relative path to your own java files.
And when you run the program, make sure your class path includes both the locations of your libraries and the location of your class files (which in this case would be the current directory):
java -cp .:libs/lib1.jar:libs/lib2.jar <MainClass>
Trying to compile and run my java program from the commandline that is set up a bit weird. The file structure is as follows:
[ROOT]/
|
|____libs/
| |____myExtraJar.jar
|
|____src/
|____main/
|____com/
|____example/
|____myClass.java
The package is defined at the top of the java file as
package com.example;
I am able to compile the program fine (I think) while in the root folder, using
javac -classpath "/libs/myExtraJar.jar" src/main/com/example/*.java
I don't get any compilation errors (such the ones that occur if I leave off the classpath) and I can see that .class files are being created in the com/example/ folder. However, I can't find any way to run the compiled program. Running
java src/main/com/example/myClass
results in the message
Error: Could not find or load main class src.main.com.example.myClass
Any help would be appreciated.
You need to specify the classpath when you run it, and you also need to use the fully-qualified classname. Like,
java -cp "libs/myExtraJar.jar:src/main" com.example.myClass
Elliot is right. More precisely, you need to add the build directory to your classpath. It is the directory containing your *.class files, and is sometimes named target/.
$ java -cp "target:lib/myExtraJar.jar" com.example.myClass
Moreover, src/main/com/example/myClass should be com.example.myClass, which is the fully-qualified class name. See http://www.manpagez.com/man/1/java/ for details of the java command.
this is a beginner question. I am having a problem running my java program from command line. I am using Windows10.
The problem is the following. I have a folder named "folder1", which is located o the dekstop of my computer. So the full path would be
C:\Users\Ioanna\Desktop\folder1
Inside that folder I have created a second folder which I named folder2. so the path to this would be
C:\Users\Ioanna\Desktop\folder1\folder2
Inside folder2 I have a java file named example.java
I want to compile it and run this file with setting the -classpath option through cmd. I dont want to set the path or to add the folder to tha path from environment variables.
I am trying
C:\Users\Ioanna\javac -cp C:\Users\Ioanna\Desktop\folder1\folder2 example.java
but it says file not found.
I tried several other alternatives, but I can't seem to find how to compile successfully the program.
Code compilation (to bytecode) and code execution are two separate steps, in Java.
First, compile your .java to obtain the corresponding .class file (I'm assuming your folder paths are right):
C:\Users\Ioanna\javac C:\Users\Ioanna\Desktop\folder1\folder2\example.java
This will give you example.class in that same folder.
Next, run that class (provided it has a main() method):
C:\Users\Ioanna\java -cp C:\Users\Ioanna\Desktop\folder1\folder2 example
java expects the path of the file(s) to compile. And example.java is not in the current folder (C:\Users\Ioanna).
Use
javac Desktop\folder1\folder2\example.java
Basically, my program compiles and runs fine in Eclipse but doesn't compile in Command Prompt. It gives me Symbol Not Found with the pointer on the name of one of my classes. I've never had this happen before- the only difference between this program and the other ones I wrote is that I made a package in Eclipse for them. Any ideas?
I think you didn't set the path correctly.
How to set Path in Java
The path is required to be set for using tools such as javac, java etc.
If you are saving the java source file inside the jdk/bin directory,
path is not required to be set because all the tools will be available
in the current directory.
But If you are having your java file outside the jdk/bin folder, it is
necessary to set path of JDK.
If you did not do it already, it might help if you remove the package declaration in the java files. If your compiling class uses any other classes, they will not be compiled because of the package declaration. It happened with me once.
In my code I have the following statement import com.apple.dnssd.*; and compiler (javac) complains about this line. It writes that the package does not exist. But I think that it could be that "javac" search the package in a wrong place (directory). In this respect I have two questions:
How can I know where javac search for the packages?
I think that it is very likely that I have the above mentioned package but I do not know where it is located. What are the typical place to look for the packages?
ADDED:
On another Windows machine I tried the same thing and the "javac" does not complain (as before I compiled without any options like "-cp"). I check values of the "classpath" environment variable. It is equal to "C:\Program Files\Java\jdk1.6.0_18\bin;.;..". I went to the first classpath directory and did not find there something that could be the "com.apple.dnssd" library (no jar files, no files containing "apple"). So, I do not understand why javac do NOT complain on the second Windows machine.
ADDED 2:
On the machine #2 I have installed Bonjour after JDK. On the machine #1 JDK was installed after Bonjour.
ADDED 3:
On the machine #1 (where I cannot import the package) I found the jar file (it is located in "C:\Program Files\Bonjour" and its name is "dns_sd.jar"). I tried to add the above mentioned directory to the PATHCLASS environment variable on Windows 7 (and I restarted the system). It does not help. I still cannot import the package. I also tried to specify the "-classpath" in the command line. It also does not help. Now I will try to reinstall Bonjour (as it was advised).
ADDED 4:
I have uninstall Bonjour and Bonjour SDK. I have reload Window. Then I have installed Bonjour and Bonjour SDK. I have reload the Window. It did not solve the problem. I still cannot import the package (javac writes that package does not exist). I have also copied the *.jar file to the same directory there the source is located. It does not work. I used "javac -cp .". It does not work. Now I am out of options. I do not know what else can I try. Can anybody help me pleas?
ADDED 5:
My classpath is: C:\Program Files\Java\jdk1.6.0_18\bin;.;..;"C:\Program Files\Bonjour"
I try to compile from this directory: C:\Users\myname\java\bonjour\example
I compile by the following command: javac ServiceAnnouncer.java
I get the following error message: ServiceAnnouncer.java:1: package com.apple.dnssd does not exist
ADDED 6:
Finally I have managed to import the library. I did it in the following way:
javac -cp "C:\Program Files\Bonjour\dns_sd.jar" ServiceAnnouncer.java
The important thing is that I have specified the jar file after the -cp (not the directory where the jar file is located). It works also if I replace "dns_sd.jar" by "*". So, my conclusion is that after the "-cp" I need to specify jar files (not directories).
Java/javac will search for classes in the classpath.
The default classpath covers the /path/to/jre/lib and /path/to/jre/lib/ext folders. Any classes and JAR files which are found there will be taken in the classpath. You can in theory put your classes and JAR files there so that you don't need to do anything to get java/javac to find them. But this is actually an extremely bad practice. It's recipe for portability trouble, because this isn't the same in all machines. Leave those folders intact.
Then there's the environment variable %CLASSPATH% wherein you can specify full paths to root folders where classes are located and/or full paths to JAR files (including the JAR file name itself!). Multiple paths are in Windows to be separated by semicolon ; and in *Nix by colon :. Paths with spaces inside needs to be quoted with "". Here's an example:
SET CLASSPATH = .;/path/to/File.jar;"/spacy path to some pkg/with/classes"
Note the period . at the beginning of the argument. This indicates the current path (the current working directory from where the java/javac command is to be executed). It will only find classes in the current path that way, and thus not JAR files! You need to specify full path for them. Since Java 1.6 you can also use wildcards to specify multiple JAR files in some path. E.g.
SET CLASSPATH = .;/path/to/all/jars/*;"/spacy path to some pkg/with/classes"
This environment variable is actually a convenience way to manage the classpath so that you don't need to type the same thing down again and again in the command console everytime. But this is only useful for new-to-java users and the cause of all future confusion because they will think that this is "the" classpath. This assumption is actually wrong and again the cause of portability trouble because this isn't the same in all machines.
The right way to define the classpath is using the -cp or -classpath argument wherein you actually specify the same information as you'd like to enter for %CLASSPATH%, i.e. (semi)colon separated and paths-with-spaces quoted, for example:
javac -cp .;/path/to/File.jar;"/spacy path to some pkg/with/classes" Foo.java
Note that when you use either -cp or -classpath (or -jar) arguments, then java/javac will ignore the %CLASSPATH% environment variable (which is actually a Good ThingTM).
To save the time in retyping the same again and again, just create a bat or cmd file (or if you're on *Nix, a sh file). Basically just put therein the same commands as you'd enter "plain" in the console and then execute it the usual platform specific way.
To save more time, use an IDE. The classpath which is to be used during both compiletime and runtime inside the IDE is called the "build path". Explore the project properties and you'll see.
http://java.sun.com/javase/6/docs/technotes/tools/windows/classpath.html
To answer your first question (How to know where javac searches for packages):
Check what your $CLASSPATH variable is set to.
echo $CLASSPATH
This is where you JRE will search for class files and resources. You can either set it as an environment variable,
set CLASSPATH=path1;path2 ...
or set it when your run javac.
C:> javac -classpath C:\java\MyClasses src_dir
(Great examples for javac are found here)
In this case, your jar file containing 'com.apple.dnssd.*' should be located in your classpath. Just download that jar, and put it in the place where your classpath is searching.
Assuming that dns_sd.jar is installed in 'C:\Program Files\Bonjour', then try to compile your code like this:
cd C:\Users\myname\java\bonjour\example
javac -classpath C:\Program Files\Bonjour ServiceAnnouncer.java
This link suggests that the JAR containing this package is part of Bonjour for Windows. Look for it there.
javac.exe only searches where you tell it with the CLASSPATH. If you don't understand how to set CLASSPATH, I'd recommend reading something like this.