能够编译但无法使用jar文件从cmd运行Java

Question

I have a java file which uses jfreechart libraries, uses a text file from local drive and displays graph. Runs fine with eclipse. However, I want to run this from cmd prompt, other simple Java files are able to run successfully via cmd prmnt but not able to run this file. PS: MyTool.java is able to compile without errors and class file is created, but not able to run.

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 1) This is how I am compiling it in cmd prompt: (gives 0 errors)

C:\Documents and Settings\hello.maga\workspace\MyTool\lib>javac -cp "gnujaxp.
jar;iText-2.1.5.jar;jcommon-1.0.16.jar;jfreechart-1.0.13.jar;jfreechart-1.0.13-e
xperimental.jar;jfreechart-1.0.13.jar;junit.jar;servlet.jar;swtgraphics2d.jar" MyTool.java

  2) This is how I am running it:


 C:\Documents and Settings\hello.maga\workspace\MyTool\lib>java -cp "gnujaxp.j
 ar;iText-2.1.5.jar;jcommon-1.0.16.jar;jfreechart-1.0.13.jar;jfreechart-1.0.13-ex
 perimental.jar;jfreechart-1.0.13.jar;junit.jar;servlet.jar;swtgraphics2d.jar" MyTool


    Error for second command: 

    Exception in thread "main" java.lang.NoClassDefFoundError: MyTool
    Caused by: java.lang.ClassNotFoundException: MyTool
    at java.net.URLClassLoader$1.run(Unknown Source)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.net.URLClassLoader.findClass(Unknown Source)
    at java.lang.ClassLoader.loadClass(Unknown Source)
    at sun.misc.Launcher$AppClassLoader.loadClass(Unknown Source)
    at java.lang.ClassLoader.loadClass(Unknown Source)
    Could not find the main class: MyTool.  Program will exit.

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What I don't understand is, if there are any errors, then it should not compile in first place, can someone educate me. Thank you very much.

Answer 1

You need to include "." in the classpath, like so:

java -cp ".;gnujaxp.jar;iText-2.1.5.jar;jcommon-1.0.16.jar;jfreechart-1.0.13.jar;jfreechart-1.0.13-experimental.jar;jfreechart-1.0.13.jar;junit.jar;servlet.jar;swtgraphics2d.jar"

Answer 2

From " Setting the class path ": "The class path tells SDK tools and applications where to find third-party and user-defined classes -- that is, classes that are not Java extensions or part of the Java platform. The class path needs to find any classes you've compiled with the javac compiler -- its default is the current directory to conveniently enable those classes to be found."

However if you set the classpath yourself, the default no longer applies, and you're expecting it to load classes from the current directory. You'll have to add it manually, like by adding "." to the class path as Ed Staub recommended.

When compiling, your class wasn't needed on the class path, so to speak, since it's what was being compiled. You only needed all the other classes (in the jar files) on the class path for that. That's why you're able to compile but not run, even though you used an identical class path for both operations.