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Java Forum / First Aid / January 2006Can't execute from command line
Hi I've been using BlueJ to learn Java and can build classes with a main method and execute them succesfully in this environment. However, I'm starting to use the command line in Windows XP and am meeting a problem... Having changed the path variable to point to jdk1.5.0_06 I can now use the javac and java commands, but I am receiving an error on the command line when I try to execute my compiled class file. Here's what I have:- Test.java: public class Test { public static void main(String[] args) { System.out.println("Hello World"); } } >javac Test.java produces no errors... >java Test produces this error:- Exception in thread "main" java.lang.NoClassDefFoundError: Test What am I doing wrong?? > Hi > [quoted text clipped - 25 lines] > > What am I doing wrong?? The first thing that comes to mind is the classpath variable. If this is not set to include the current working directory, your class (Test) cannot be found, and therefor you will not be able to run your program. Try this: java -cp . Test instead of java Test -cp sets the classpath, and . is your current working directory. Best regards, JC -- http://jcsnippets.atspace.com a collection of source code, tips and tricks >> Hi >> [quoted text clipped - 48 lines] > http://jcsnippets.atspace.com > a collection of source code, tips and tricks Thankyou, that does work. However, as I am executing these commands from the directory containing the Test files, how come "javac Test.java" works, but "java Test" doesn't? >, how come "javac Test.java" works, but >"java Test" doesn't? because javac is looking for the unqualified name of a source file and java.exe is looking for the a fully qualified class name. Javac does not look on the classpath. Java.exe does.  SignatureCanadian Mind Products, Roedy Green. http://mindprod.com Java custom programming, consulting and coaching. > Thankyou, that does work. However, as I am executing these commands from the > directory containing the Test files, how come "javac Test.java" works, but > "java Test" doesn't? Because they are looking for different things. javac.exe looks for files to compiler, whereas java.exe looks for classes which it can execute. And to find those classes, java.exe looks at the classpath. Regards, JC -- http://jcsnippets.atspace.com a collection of source code, tips and tricks >> Thankyou, that does work. However, as I am executing these commands from > the [quoted text clipped - 7 lines] > which it can execute. And to find those classes, java.exe looks at the > classpath. It just seems strange, and annoying, that java.exe doesn't look for those classes in the directory it is being executed in. The Win XP command line works by looking in the current directory AND the path variable, so why can't java.exe follow the same standard? Ah well, gripe over... > >> Thankyou, that does work. However, as I am executing these commands from > > the [quoted text clipped - 12 lines] > works by looking in the current directory AND the path variable, so why > can't java.exe follow the same standard? Ah well, gripe over... Hi James, Well, it may seem strange at first, and even annoying, but the fact of the matter is that there really is a difference. And this difference explains the behaviour you are experiencing now. Files and directories are different concepts than classes and packages. You mentioned yourself that the Win XP command line uses the current directory and the path variable, well, the classpath variable for java.exe can be compared to the path variable for the Win XP cli. But the Win XP cli only works for Win XP, while Java (the language) is intended to be run on *any* system (that is, any system for which a JVM is available). Anyway, there is a simple way to solve all this: just like you can adjust the path variable, you can adjust the classpath variable. I'm on Win2k at the moment, but I suspect XP to be about the same - look in settings/control panel/system, then click the advanced tab, then the environment variables button, and look for CLASSPATH under system variables. Click edit, and add ;. to the classpath variable. Then click ok, etc... to save this setting. From now on, you'll be able to use java SomeClass without having to use -cp . in the command line. Regards, JC ps: I hope this post made some sense, I feel like falling asleep any minute now :) -- http://jcsnippets.atspace.com a collection of source code, tips and tricks Just googled and found http://www.kevinboone.com/classpath.html which seems to explain the maddening but no doubt logical situation. Many thanks for your prompt help. Regards James > Just googled and found http://www.kevinboone.com/classpath.html which seems > to explain the maddening but no doubt logical situation. [quoted text clipped - 3 lines] > Regards > James It may explain it, but it also proceeds to approve of using the CLASSPATH variable. Sun rightly advises NOT to use the system-wide variable. SignatureSteve W. Jackson Montgomery, Alabama >NoClassDefFoundError see http://mindprod.com/jgloss/caq.html http://mindprod.com/jgloss/gettingstarted.html SignatureCanadian Mind Products, Roedy Green. http://mindprod.com Java custom programming, consulting and coaching. Free MagazinesGet these publications absolutely FREE for up to 12 months. There are no hidden fees and no obligation. Simply choose a title, complete the application form and submit it. Read more ...
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