Eclipse on OS X El Capitan Error: Could not find or load main class

Question

I recently updated my MacBook Pro to El Capitan and now none of my Java code runs in Eclipse.

Every time I try to run any program I get the error:

Error: Could not find or load main class sim.app.geo.MK_3.MK_3WithUI

I have Googled and followed the guidance on StackOverflow here, here and here including:

• cleaning and rebuilding the project
• checking Run Configurations have the correct Project and Main class details
• removing all old run configurations and trying again
• adding the bin directory for the project
• checked all jar files are available
• reordering build class entries

None of the above has helped.

I'm pretty sure my Java Build Path details are in order:

Details:

• Eclipse Luna Service Release 2 (4.4.2)
• Mac OS X El Capitan v. 10.11.4
• Java jdk1.8.0_45.jdk: /Library/Java/JavaVirtualMachines/jdk1.8.0_45.jdk
• .jar files saved in /Library/Java/Extensions/ and /Library/Java/Test Backup/
• Eclipse Workspace: /Volumes/JetDrive/Drive/workspace/EngDModelOne

Answer 1

I think I've fixed this problem and if anyone else has the same problem, here's what I did.

• I removed all the references to my old JAR files from my Project libraries
• I cleaned all my projects and rebuilt them. I then restarted Eclipse.
• I downloaded all the new versions of my JAR files from here and replaced the old ones in my Java Library folders.
• I updated all my Project Libraries with the new JAR files and referenced the new Java JDK/JMF etc
• I cleaned all my projects and rebuilt them. I then restarted Eclipse.

Huzzah! Everything now works! From 3000+ errors to none and working projects.