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JVM Manager

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©1996-2017 Roedy Green of Canadian Mind Products

Disclaimer

This essay does not describe an existing computer program, just one that should exist. This essay is about a suggested student project in Java programming. This essay gives a rough overview of how it might work. I have no source, object, specifications, file layouts or anything else useful to implementing this project. Everything I have prepared to help you is right here.

This project outline is not like the artificial, tidy little problems you are spoon-fed in school, when all the facts you need are included, nothing extraneous is mentioned, the answer is fully specified, along with hints to nudge you toward a single expected canonical solution. This project is much more like the real world of messy problems where it is up to you to fully the define the end point, or a series of ever more difficult versions of this project and research the information yourself to solve them.

Everything I have to say to help you with this project is written below. I am not prepared to help you implement it; or give you any additional materials. I have too many other projects of my own.

Though I am a programmer by profession, I don’t do people’s homework for them. That just robs them of an education.

You have my full permission to implement this project in any way you please and to keep all the profits from your endeavour.

Please do not email me about this project without reading the disclaimer above.

The three versions of the Java Plug-In interfere with each other. In theory you can have only one of them installed at a time. However, you need all three for testing. The simplest version of program would effectively hide two out of the three at any one time, by fiddling with registry entries.

Other JVMs (Java Virtual Machines) interfere with each other since they may each set the classpath or path a different way. In a similar way, you want to hide all but one of them so they cannot interfere with each other.

For more of a challenge, allow each App to provide a properties file that lists the JVMs it prefers to run under and the class files it needs pre-installed and the URLs (Uniform Resource Locators) where you can get them if necessary. Your job is to set up its preferred environment and hide the others. Unfortunately, this limits you to running one JVM (Java Virtual Machine) at a time. See installing Java for more details.

One extra wrinkle is to check on the web for the latest properties file, so that you know if you must update the App itself as well as any auxiliary files.

You need to install various versions of the Plug-in, ensure they work and study the registry to see what changes the installer makes. Norton Utilities for Windows used to include a utility for noticing registry changes. I’m not sure if they still ship it. You could also detect registry changes by regedit-exporting the registry to text format and using a standard diff utility.

Your program has to effect these same changes. Java can’t twiddle the registry directly. You must use a native class written in C or C++ that uses the Windows registry fiddling API (Application Programming Interface) calls. InstallShield for Java has facilities to fiddle the registry. That would be a way to kludge it.

Look at these entries in the registry:

My computer\HKEY_CURRENT_USER\Software\JavaSoft\Java Plug-In
My computer\HKEY_LOCAL_MACHINE\Software\JavaSoft\Java Development Kit
My computer\HKEY_LOCAL_MACHINE\Software\JavaSoft\Java Runtime Environment
My computer\HKEY_LOCAL_MACHINE\Software\JavaSoft\Java Plug-In The other thing this utility would do is back up the registry and restore it or recreate it from first principles if it ever becomes damaged, a frequent event.

You also want to switch environment variables such as classpath and JIKESPATH.

For a rough and ready manager you could use regedit that has the ability export and import parts of the registry. You take snapshots and just switch between snapshots.

environment
registry
reinstaller: student project
sanity checker

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