Finding your java program - the CLASSPATH variable

Archive - Originally posted on "The Horse's Mouth" - 2009-04-02 17:02:23 - Graham Ellis
When you run a Java 'program' (strictly, the main method of a class), it looks for that class in a file with the name given and with a .class extension in the places listed in the CLASSPATH environment variable. Failure to have the right CLASSPATH set results in a spectacular series of error messages!

[trainee@easterton ~]$ java Nother

Exception in thread "main" java.lang.NoClassDefFoundError: Nother

Caused by: java.lang.ClassNotFoundException: Nother

  at java.net.URLClassLoader.run(URLClassLoader.java:200)

  at java.security.AccessController.doPrivileged(Native Method)

  at java.net.URLClassLoader.findClass(URLClassLoader.java:188)

  at java.lang.ClassLoader.loadClass(ClassLoader.java:307)

  at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:289)

  at java.lang.ClassLoader.loadClass(ClassLoader.java:252)

  at java.lang.ClassLoader.loadClassInternal(ClassLoader.java:320)

[trainee@easterton ~]$ export CLASSPATH=/home/trainee/a9tom

[trainee@easterton ~]$ java Nother

*** I love Trowbridge ***

*** I am a bit crazy ***

*** 1 => 2 ***

[trainee@easterton ~]$

Note:

CLASSPATH may include a series of : separated directories (; on windows)

CLASSPATH may contain the names of jar files, in which case the class will run straight from the jar

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Finding your java program - the CLASSPATH variable