Not able to run Eclipse Application. Can't even start Eclipse IDE

Question

I have an RCP product which doesn\'t run. Then I installed Eclipse freshly, and when I open Eclipse.exe it doesn\'t open Eclipse IDE. I get the error: NoClassDefFoundError:

Answer 1

Then I installed Eclipse freshly, and when I open Eclipse.exe it doesn't open Eclipse IDE

The same eclipse archive when unzipped on a different machine works fine

That should mean a workspace issue: eclipse try to recreate a view for which the jar is missing.
Try to launch your eclipse with '-clean' option, and making sure it does reference a fresh new workspace (with the -data option, like illustrated in this eclipse.ini)

This question illustrated a clean start:

eclipse.exe -clean --launcher.ini path\to\my_eclipse.ini

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Regarding QTP, check this article from IBM, which describes a similar situation.

In this scenario HP Mercury Quick Test Pro Professional v9.3 was installed and the following Microsoft Windows XP User and System Environmental variables were present:

IBM_JAVA_OPTION and _JAVA_OPTION

Each was set to:

-Xrunjvmhook -Xbootclasspath/a:C:\PROGRA~1\HP\QUICKT~1\bin\JAVA_S~1\classes;C:\PROGRA~1\HP\QUICKT~1\bin\JAVA_S~1\classes\jasmine.jar

or more explicitly:

-Xrunjvmhook -Xbootclasspath/a:C:\PROGRA~1\HP\QuickTest Professional\bin\java_shared\classes;C:\PROGRA~1\HP\QuickTest Professional\bin\java_shared\classes\jasmine.jar

Note: HP Mercury Diagnostic Tool is another product that used these environment variables in the past. Contact HP Support if up to date information and support is needed on their products.

However it is important to stress the focus is on these environment variables being used dangerously by any vendor product or any software or user in general setting them directly

Resolving the problem
Delete or clear the values of the IBM_JAVA_OPTION and _JAVA_OPTION variables.

After deleting/clearing the environment variables, it should be possible to start Rational Application Developer or other IBM SDK for Java (== JDK) based product.

Note: Deleting or clearing these variables may prevent the other products (such as the aforementioned HP products) from working.

Warning: Deleting or clearing or changing IBM_JAVA_OPTION or _JAVA_OPTION should be done with caution if these are needed settings. There are legitimate and safe uses of these environment variables to set JVM options.

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If this is indeed the case, that reminds me of my answer to the question:

"Why doesn’t the Java SDK installer set JAVA_HOME?"

;)

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If you want both eclipse and QTP to coexist, you need to make sure any running configuration you may have (in or outside eclipse) needing to run "with" QTP are the scripts which set those extra variables (_JAVA_HOME or other).
If those variables are set globally (by the QTP installation process itself)... bad things can happens.