Finding your java program - the CLASSPATH variable

For 2023 - we are now fully retired from IT training.
We have made many, many friends over 25 years of teaching about Python, Tcl, Perl, PHP, Lua, Java, C and C++ - and MySQL, Linux and Solaris/SunOS too. Our training notes are now very much out of date, but due to upward compatability most of our examples remain operational and even relevant ad you are welcome to make us if them "as seen" and at your own risk.

Lisa and I (Graham) now live in what was our training centre in Melksham - happy to meet with former delegates here - but do check ahead before coming round. We are far from inactive - rather, enjoying the times that we are retired but still healthy enough in mind and body to be active!

I am also active in many other area and still look after a lot of web sites - you can find an index ((here))

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$1.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
(written 2009-04-02)

Associated topics are indexed as below, or enter http://melksh.am/nnnn for individual articles

J601 - Java Introduction
  [25] Release numbers - (2004-08-23)
  [111] Training notes available under Open Distribution license - (2004-11-07)
  [124] PHP v Java - (2004-11-20)
  [317] Programming languages - a comparison - (2005-05-20)
  [792] Is Java the right language to learn? - (2006-07-04)
  [871] Java oversold? - (2006-09-19)
  [1049] Java 6, Apache Tomcat 6. - (2007-01-21)
  [1158] Private Java Course - A customer's pictures - (2007-04-22)
  [1418] A Golf Club Decision - Perl to Java - (2007-11-01)
  [1466] Effective Java training - the bootcamp approach - (2007-12-09)
  [1497] Training Season Starts again! - (2008-01-07)
  [1557] Trying out our Java examples on our web site - (2008-02-27)
  [1766] Diagrams to show you how - Tomcat, Java, PHP - (2008-08-22)
  [1908] Java CLASSPATH explained - (2008-11-26)
  [2423] What is a JVM, a JRE, a JDK - components of the core Java Environment - (2009-09-26)
  [2536] All the Cs ... and Java too - (2009-12-13)
  [4332] First Java Application - calculating the weight of a tablecloth - (2014-11-29)

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This is a page archived from The Horse's Mouth at http://www.wellho.net/horse/ - the diary and writings of Graham Ellis. Every attempt was made to provide current information at the time the page was written, but things do move forward in our business - new software releases, price changes, new techniques. Please check back via our main site for current courses, prices, versions, etc - any mention of a price in "The Horse's Mouth" cannot be taken as an offer to supply at that price.

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