Develop Reference

How to import JAVA packages in cmd?

This is the first time I am compiling a program, and it doesn't seem to be working out. Looks like some packages are not being located - so for this question, I'll just focus on one:
Steps I've take so far:
1) setting up the System Variable Path to include java
2) in CMD.exe: jar tf log4j.jar I did this to make sure it includes log4j.Logger and it does.
3) I Shift+rightclick and open command prompt from this folder:
4) Then I enter javac TNT.java and i get the following error (along with others):
Any thoughts?
I set the classpath to the same folders with set classpath = "name of folder" no change...
edit
5) have also tried
javac -cp jdkbindirectory;jrebindirectory;theabovefolder TNT.java
I get this:
blahblahblah

You shouldn't set the classpath using an environment variable as it is bad practice. What if you accidentally change it later for a different project and your current project breaks?
When including classes in the classpath, you can include the path of the root of the package of the class, as in the folder that contains the folders in the package structure. However, when you're including a jar in your classpath, you need to put the entire path of the jar file (relative to the current working directory) all the way up to the jarname.jar.
Also, remember that by default, java looks in the current working directory and uses that as its default classpath. However, as soon as you specify a classpath it no longer does that automatically for you. Be sure that you're including your current directory in your classpath as well.
Finally, be sure to surround the classpath in quotes otherwise java might think its a part of another argument.
I would try this:
javac -cp "./;log4j.jar" TNT.java
And then to execute the class file:
java -cp "./;log4j.jar" TNT
Hope this works, good luck!

How to compile with a bash script a multipackaged java project that uses jar file

I am developing a project for my Computer Network course.
Actually I ended it, now I need to write a script to compile it, so the teacher will be able to run it
I developed with Netbeans and now I am struggling to compile it by command line.
I have 3 folders (packages)
client: classes of the client process
server: classes of the server process
sharedClasses: classes usefull to both client and server (like User.java)
Also I am using the Gson as a jar file which is needed in the sharedClasses package
for example in sharedClasses there is a class called Message that uses Gson to be transformed in a json string
I tried a lot to create a script that compile it all but every time I get "ClassNotFoundException" or stuff like that: the online guides to understand classpath and so on are pretty bad.
Can someone tell me how to do my script and explain why things are done the way they are? Thanks

Path variables are a concept in all Unix and Windows operating systems. They are not a Java invention, but Java bases its own classpath and module path concepts on them.
A path variable’s value is simply a string which contains a list of file locations, separated by a colon (:) in Unix or a semicolon (;) in Windows.
The most common path variable is simply PATH. (I believe that in Windows, the variable’s canonical name is Path, but environment variables are case-insensitive in Windows, so it can be referred to as PATH in most cases.)
When you try to execute a program on the command line, by specifying a command name with no directory components, the operating system checks each file location in PATH, in order, and for each location which is a directory, the system will look for a match there. The first match is the one the operating system uses.
Java borrows this concept for the classpath. In the very early days of Java, it was exactly the same: If your classpath were /home/giulio:/opt/libraries, and you were looking for a class named com.example.ConnectionFactory, Java would look for a compiled file named com/example/ConnectionFactory.class in /home/giulio and then in /opt/libraries.
It wasn’t long before the classpath was allowed to contain files which are compressed archives of classes, in addition to directories. Your classpath might contain /home/giulio:/opt/libraries/foolib.jar, in which case Java would first check for a requested class in /home/giulio, since that is a directory, and if that failed, it would look for a matching entry in the /opt/libraries/foolib.jar archive file. (Zip files are also acceptable, and in fact a .jar file is really just a zip file with a few special Java-specific entries.)
So, when you want to tell Java to look in certain places for libraries, specify them in the classpath.
For instance, when compiling your client code:
projectroot=`dirname "$0"`
javac -classpath "$projectroot"/sharedClasses/classes \
-d "$projectroot"/client/classes \
"$projectroot"/client/src/*.java
When you run your code:
java -classpath "$projectroot"/sharedClasses/classes:"$projectroot"/client/classes \
edu.acme.giulio.client.Main

Write a batch file that starts a java program

So I have a java project with multiple java files.
I know that is almost straight forward to start a java application using batch file. But that is for a pretty simple java program with a single class.
However I am wondering if it is possible to do that with in a scale of a project that you usually create using eclipse. A large project with multiple packages, classes and multiple java files.
My try was to write a script and apply on the main class as following
set path = C:\Program Files\Java\jdk1.7.0_25\bin
javac -classpath twitter/twitter4j-stream-3.0.5.jar;twitter4j-core-3.0.5.jar" sourcepath="lib/twitter4j-core-4.0.1.jar;lib/twitter4j-core-4.0.1.jar;lib/twitter4j-stream-4.0.1.jar;svm_light_lib Program.java
java Program
However when I start the .bat file it automatically closes.
Any Ideas ?
Thanks in advance

First, never overwrite the environment variable path, not even
temporarily. Append your folder instead: set "path=%path%;%mypath%" or set "path=%mypath%;%path%".
(There exists a particular path command but I'm not sure about right syntax: path=%path%;%mypath% with = assignment or path %path%;%mypath% without it).
Use full path to a program if you know it, e.g. "%mypath%\javac".
For better readability, values for -classpath and -sourcepath options are stored to the environment variables mycpth and mysrcp, respectively. Note and use proper " quotation and no spacing around = to avoid any leading and trailing spaces in all set commands.
pause to see all the javac output. Displays the message Press any key to continue . . .
Next code should be (syntax) error-free. However, success depends (among others) on classpath and sourcepath entries visibility as well...
set "mypath=C:\Program Files\Java\jdk1.7.0_25\bin"
set "path=%path%;%mypath%"
set "mycpth=twitter/twitter4j-stream-3.0.5.jar;twitter4j-core-3.0.5.jar"
set "mysrcp=lib/twitter4j-core-4.0.1.jar;lib/twitter4j-core-4.0.1.jar;lib/twitter4j-stream-4.0.1.jar;svm_light_lib"
"%mypath%\javac" -classpath "%mycpth%" -sourcepath "%mysrcp%" Program.java
pause
java Program

However I am wondering if it is possible to do that with in a scale of a project that you usually create using eclipse. A large project with multiple packages, classes and multiple java files.
Of course it is possible!
In this case, I suspect the problem is that you java command doesn't have a "-cp" argument. The java command is probably failing because it can't find twitter classes ... at runtime.
Remember to include "." on the classpath ... or else java won't find the file that you just compiled.
#JB Nizet's suggestion is also very important advice for finding out what is actually happening.

How to config where Syntastic is going to generate the .class files?

I am writing some code to my phd project and I am using VIM as my code editor.
As I am coding in Java, I chose Syntastic to check and compile my code. So far so good.
My issue comes when I try to create a directory with all my .classes. I want to do this, because then I intend to create a .jar using this directory using a simple make file. So, this is my scenario:
source code:
C:\Users\LABIMD05\workspace\backhoe-nomvn2\src (all .java)
class files:
C:\Users\LABIMD05\workspace\backhoe-nomvn2\bin\classes (where I want to put all the .classes)
In this way, let's say I am coding br.ufrn.Project. When I use :SyntasticCheck, I want the br.ufrn.Project .class file to be generate at:
C:\Users\LABIMD05\workspace\backhoe-nomvn2\bin\classes\br\ufrn\Project.class
and not at:
C:\Users\LABIMD05\workspace\backhoe-nomvn2\src\br\ufrn\Project.class (the same of the .java)
Here goes the options that I am using at my _vimrc file
let g:syntastic_java_javac_classpath = 'C:\Users\LABIMD05\workspace\szz_lib\*;C:\Users\LABIMD05\workspace\backhoe-nomvn2\bin\classes'
let g:syntastic_java_javac_delete_output = 0
let g:syntastic_always_populate_loc_list = 1
let g:syntastic_mode_map = { 'mode': 'passive',
\ 'passive_filetypes': ['java']}
THE PROBLEM:
Everytime I compile br.ufrn.Project file, the .class file goes to the same directory of the .java file
I thought it would be because Syntastic would create the .class file in the current working directory. Then I used:
cd C:\Users\LABIMD05\workspace\backhoe-nomvn2\bin\classes
To see if Syntastic would create the .class in the desired place. But I had no success.
Would you guys have some clue where can I configure it? I just want to separate the .class files from .java files and then use a make file to create a jar with the binaries only. Simple thing.
Thank you for any help you can provide.

You can't configure Syntastic to compile the java files to a different location. However, you can make a command that uses SyntasticCheck and compiles the java files to a different directory.
Using the javac -d dir File.java command you can tell the java compiler where to generate .class files.
Using this you can make a vim command, I called it Javac but you can choose what to call it. It will call Syntastic check and generate the .class files to the other file.
function! Javac()
execute "w"
execute "SyntasticCheck"
execute "!javac -d C:\Users\LABIMD05\workspace\backhoe-nomvn2\bin\classes %"
endfunction
command! Javac :call Javac()
If the SyntasticCheck part is not necessary you can remove that.
Just put this in your .vimrc and then you can use :Javac to execute it.
Alternatively you could also put it in ~/.vim/ftplugin/java.vim if you want it to only be active when editing the java filetype.

What exactly is a class path in java?

I wrote a program that works on my laptop perfectly, but I really want it to work on a server that I have. Using NetBeans, I've clean and built the project. I copied the contents of the folder dist on my server but I cannot seem to get to work by using command
java -jar nameOfFile.jar
I get the error
java.lang.NoClassDefFoundError: org/....
I have been doing some reading and from what I gather is that I need to pretty much specify where the libraries that I've used are located. Well they are located in a subfolder called lib.
Question:
So what would I need to do in order to be able to run my jar?

CLASSPATH is an environment variable that helps us to educate the Java Virtual Machine from where it will start searching for .class files.
We should store the root of the package hierarchies in the CLASSPATH environment variables.
In case of adding or using jar libraries in our project, we should put the location of the jar file in the CLASSPATH environment variable.
Example: If we are using jdbc mysql jar file in our java project, We have to update the location of the mysql jar file in the CLASSPATH environment variable. if our mysql.jar is in c:\driver\mysql.jar then
We can set the classpath through DOS in Windows
set CLASSPATH=%CLASSPATH%;c:\driver\mysql.jar
In Linux we can do
export CLASSPATH=$CLASSPATH:[path of the jar]
Hope it helps!

Try that:
java -classpath "$CLASSPATH:nameOfFile.jar:lib/*" path.to.your.MainClass
What this does is setting the classpath to the value of $CLASSPATH, plus nameOfFile.jar, plus all the .jar files in lib/.

Classpath
A compiler(e.g. javac) creates from .java - .class files and JVM uses these .class files.
classpath - local codebase[About] - points on the root of source. classpath + import_path = full path
For example for MacOS
//full path
/Users/Application.jar/my/package/MainClass
//classpath
/Users/Application.jar
//import_path
my.package.MainClass
Android classpath
ANDROID_HOME/platforms/android-<version>/android.jar
//e.g
/Users/alex/Library/Android/sdk/platforms/android-23/android.jar

When you use a META-INF/MANIFEST.MF file to specify the Main-Class dependencies must be specified in the manifest too.
The -jar switch ignores all other classpath information - see the tools docs for more.

You need to set class path using
The below works in bash .
This is temporary
set CLASSPATH=$CLASSPATH=[put the path here for lib]
If you want it permanent then you can add above lines in ~/.bashrc file
export CLASSPATH=$CLASSPATH:[put the path here for lib]:.

You have 2 questions, one is the "title question" and another is the "foot note question" after elaborating your problem.
Read this documentation bellow to get a better understanding of CLASSPATH.
https://docs.oracle.com/javase/tutorial/essential/environment/index.html
https://docs.oracle.com/javase/8/docs/technotes/tools/windows/classpath.html
This is fast and straight forward for what you need.
For your first question, this will do:
The documentation recommends us to set a classpath for every application we are running at the moment using (use in the command-line):
java -classpath C:\yourDirectoryPath myApp
For your second question, look this exercise in the java documentation. It seems to be the same problem:
https://docs.oracle.com/javase/tutorial/essential/environment/QandE/answers.html
Answers to Questions and Exercises: The Platform Environment
Question 1.A programmer installs a new library contained in a .jar file. In order to access the library from his code, he sets the CLASSPATH environment variable to point to the new .jar file. Now he finds that he gets an error message when he tries to launch simple applications:
java Hello
Exception in thread "main" java.lang.NoClassDefFoundError: Hello
In this case, the Hello class is compiled into a .class file in the current directory — yet the java command can't seem to find it. What's going wrong?
Answer 1. A class is only found if it appears in the class path. By default, the class path consists of the current directory. If the CLASSPATH environment variable is set, and doesn't include the current directory, the launcher can no longer find classes in the current directory. The solution is to change the CLASSPATH variable to include the current directory. For example, if the CLASSPATH value is c:\java\newLibrary.jar (Windows) or /home/me/newLibrary.jar (UNIX or Linux) it needs to be changed to .;c:\java\newLibrary.jar or .:/home/me/newLibrary.jar."