When trying to run the following command to compile some_file.java in Windows
javac -classpath "some_class_path" "some_file.java"
it fails, telling me I didn't pass it any source files.
If instead I make
cd "some_class_path"
javac -classpath "some_class_path" "some_file.java"
it works fine. Why? This bothers me as I want to compile a set of .java files from my program through javac.
It would help if you could be more concrete about your description, but it looks like you're expecting the classpath to be used to look for the files you specify on the command-line as well. It doesn't work that way - the source files you specify must be the exact paths to those files.
Try to use full path to java source file. Anyway, could you provide exact commands and exceptions?
This is not the usage of the classpath. The classpath option specifies where to find the dependencies, not the source files. Just compile using:
javac "path\file"
(windows version)
I don't think I see any obvious reason why that wouldn't work but then work if you're in that directory. Maybe quotes don't work the way I think they do in Windows. Either way, I suggest that you look at Ant, as it is the industry standard way to compile a set of java files.
Related
I have a simple MyHelloWorld.java file within a directory myhelloworld. I set the classpath to appropriate direcotries by exporting CLASSPATH='[some needed class]' in my ~/.bashrc file. and I still need to use javac MyHelloWorld.jaca -cp 'the above classpath' to compile the .java file.
So here's my first question, why do I still need to explicitly set classpath by having a -cp option given the CLASSPATH is already specified?
After the file was compiled, I saw no file like MyHelloWorld, but the java commmand can autocomplete 'java MyHelloWorld' when in fact there's no file named MyHelloWorld exists within the directory? (If I typed "java MyH", the command can be automatically completed).
When I tried to execute 'java MyHelloWorld', it prompted me there's NOClassDefFoundError, which was an indicator of missing library. However when I tried to do 'java -cp MyHello', The command wouldn't complete itself, suggesting it couldn't find anything executable at all
So what are the reasons for above confusing signs. Can anyone take from here and explain to me how java deal with classpath and package, etc. Thanks!
Follow the java tuturial and especialy this section.
The section about JARs is for you too.
I have just downloaded a third party java library which i need for a program i'm about to create.
But i can't figure out how to actually install the library so that i can literally type
import path.to.library;
in my java class file without having any errors.
I have looked at many tutorials and answers on StackOverflow but each of them seems to include the use of some or the other IDEs for java.
Well, i'm a bit rustic and would like to know how to make it work with notepad and the command line, coz that's what i use to make a program.
When you are compiling, include the following in your line:
-classpath nameOfJar.jar
However, once you actually switch to use an IDE, you will see the multiple benefits this approach can bring.
You don't specify a path in the import statement, just the package name.
All usable JAR files have to be specified in the classpath on commandline when starting your Java program.
You need to understand how Java's classpath works. For a comprehensive description, read the Oracle manual page on this topic. Alternatively the PATH and CLASSPATH page of the Java Tutorial.
(FWIW - it is generally considered to be a bad idea to use the CLASSPATH environment variable to set the classpath, because this is liable to lead to "nasty surprises" if you deal with software that requires different classpaths.)
If you don't use any IDE you won't have code complete. However if you know all the packages/classes/methods names/signitures you can use pure Notepad and then compile it by adding the library to your classpath (eg. using the -cp switch in the javac command when compiling)
JARs are not required to be installed. They required to be accessible at compile- and run- time. You can add jar by command line parameter or CLASSPATH environment variable. IDEs have special means for setting JAR;s location in visual manner.
You'll need to be more specific about what you have tried so far. This generally isn't something complex though, if you want to manually invoke the compiler you would do something like
javac -cp somejar.jar myclass
Once you get used to this process, it's better to automate it using a build tool such as ant or maven. Ant is a little easier to begin with, maven has some additional capabilities that make it a little more complex.
Pretty basic problem here. So I have a Java package that I have created that has three classes (one has the main method). I am trying to use a few Apache Jars, and have added these to my build path in Eclipse. However Eclipse wont let me build and run it properly, so I am trying the command line. I have added the env var CLASSPATH and pointed it to my lib directory which hold the Apache Jars. However, when I try to use javac I get a bunch of errors:
package org.apache.xmlrpc does not exist
import org.apache.xmlrpc.client.XmlRpcClient;
I was reading the man page for javac and it said that:
If neither CLASSPATH, -cp nor -classpath is specified, the user class path consists of the current directory.
So I tried copying the Jars to the same location as my three source files, but no change.
Can someone please tell me what I'm doing wrong?
Thanks.
Classpath variable (or command line option of javac) must contain all jars explicitly. It cannot go through jar files stored in specified directory.
You can compile this by specifying the option -cp on the command line:
javac -cp foo.jar:bar.jar foo/bar/Baz.java
You then run it with the same option:
java -cp foo.jar:bar.jar foo.bar.Baz
It sounds like you've just set the classpath to the directory containing the jar files. You need to set it to the individual jar files, or use java.ext.dirs to set an "extension" directory containing jar files. I'd recommend using the specific jar files. Something like:
// Assuming Windows...
CLASSPATH = c:\libs\foo.jar;c:\libs\bar.jar
I'd also personally recommend specifying the classpath on the command line instead of using an environment variable - the latter will work, but it ends up being a bit more fiddly if you want to compile different projects against different libraries.
However, I'd actually recommend getting Eclipse working first, rather than retreating to the command line. It should be fine - if you could give us more information about what's failing in Eclipse, we may be able to help you with that instead.
The jar files in the current directory are not automatically included; that only refers to .class files in normal package/directory hierarchy. Jar files must be added either explicitly, or via a wildcard like javac -cp ./* (Assuming JDK6+)
(Some OSes may require an escape of the * to avoid globbing; OSX does not.)
I agree with previous answers, but I would also recommend to use proper java build tool - like ant (perceived easier to use, but not necessary) or maven ( perceived more difficult to use, but really worth learning )
COMPLETE EDIT BUT SIMILAR PROBLEM
What's the best software/plugin to enable FTP on Eclipse? I'm using FileZilla, but is there something better/easier?
You are telling javac to compile gamedata.txt and it is reporting an error that it cannot compile this file.
I'd highly suggest using a tool like Ant to script your compilation/packaging/etc so you don't have to worry about typing in arguments on the command line.
First of all, the -J command line argument is not meant to be literally passed as -J<flag>. Taken directly from the javac man page (you can view the exact same thing by typing man javac into the shell):
-Joption
Pass option to the java launcher called by javac. For example,
-J-Xms48m sets the startup memory to 48 megabytes. Although it
does not begin with -X, it is not a `standard option' of javac.
It is a common convention for -J to pass options to the underly-
ing VM executing applications written in Java.
Really, if you want to make this an executable, you can just use the tools that exist in Eclipse to make an executable. Using the command-line javac adds an extra level of complexity that is unnecessary, and that Eclipse is specifically designed to remove.
In eclipse, you can (I think) use File->Export->Java->Executable JAR File to make your project into an executable JAR that any computer with the Java Virtual Machine can run. That way, your project will work on both your computer and the Unix system at your school. You may have to add gameData.txt manually to the JAR or include it separately in the package, not sure how Eclipse does that type of thing though.
You can only compile .java files. If you remove the .txt file from the list of files to compile, it should work fine. If you want to compile all the files in a directory, you can simply use javac *.java
There are some examples in the javac synopsis.
Edit: Updated link to Solaris examples, which are similar to Linux.
I downloaded the Javax.mail package. I have jdk1.6.0_11.
Problem is...I cannot get javac or java to find those classes!
I can get apps to compile using JCreator LE ( by adding the mail jar
to its search list ) but, when I try to run the app in a command window,
it fails.
Can I add these new classes to the rt.jar without
hurting my jdk installation?
I know java has it wired up to look there for classes.
(And, the mail classes are inside a javax package - seems like
they could reasonably be added to the javax folder in rt.jar..
Thanks!
Phil D'
No you can't, nor should you.
Instead, figure out the problem with your classloader (probably paths?). You'll need that for the next library you need to access.
Messing with rt.jar means you can't run on any other JVM.
You should either specify the jar file in your classpath: preferably on the command line with the -cp option, but possibly with the CLASSPATH environment variable.
Alternatively, you can specify its directory in the java.ext.dirs system property. For more details, see the documentation for the extensions mechanism.
You shouldn't be messing around with rt.jar. That's very definitely not the way to make extra jar files available - it's akin to trying to add Microsoft Word to the Windows kernel ;)
Adding things to rt.jar seems like a bad idea, even though its possible and easy to accomplish.
Try compile your application from the command line like this:
javac -cp <path_to_3rd_libs>/jarfile.jar . MainClass.java
If the compiler still complains about the javax.mail package try to unpack/examine the jar file to see that javax.mail package (and its expected content) is there.
(On windows its easy to examine a jar file using 7zip.)
Most definitely no.
If you post the command you are running from the command line we will be able to point you on the right direction, but most likely you are just missing a classpath parameter.
java -classpath /path/to/mail.jar MyClass
You need to understand the CLASSPATH concept which allows you to add individual classes and jar files containing classes to the "universe" of defined classes available for the code you want to compile and/or run. It is similar in idea to the PATH variable in the Windows world.
For the Windows command line this is the documentation:
http://java.sun.com/javase/6/docs/technotes/tools/windows/classpath.html
The Java Tutorial surprised me by not being well-written for this particular concept:
http://java.sun.com/docs/books/tutorial/essential/environment/paths.html
You most likely need something along the lines:
C:> set CLASSPATH=c:\javamail\first.jar;c:\javamail\second.jar
after which both java and javac should know about these classes