There may be one Java installation - library, etc. but each time you start a Java program it gets its own jvm instance. There may be shared library components but that is managed by the operating system.
Using the right words is important.
Joined: Mar 22, 2005
Instead of running two Tomcat instances, it's possible to have a single instance listen on two different ports, thereby still having just a single server process. Not sure if that would help in your circumstances. For that you'd need additional Connector elements inside the Service element in your server.xml. See http://tomcat.apache.org/tomcat-5.5-doc/config/index.html for more details.
subject: Multiple Tomcat on Same Machine(One JVM) + Total Initial Heap Size