Error con java, tomcat, servlet

[una_xikilla]

Lo he intentado con un simple "hola mundo" y me pone lo siguiente:

C:\Program Files\Apache Software Foundation\Tomcat 7.0\webapps\CasaRural>java -c
lasspath "C:\Program Files\Apache Software Foundation\Tomcat 7.0\lib\servlet-api
.jar" holamundo.java
Exception in thread "main" java.lang.NoClassDefFoundError: holamundo/java
Caused by: java.lang.ClassNotFoundException: holamundo.java
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: holamundo.java. Program will exit.