I am unable to launch modded Minecraft using the latest Minecraft Launcher with Java 10. I am reporting this bug in the Mojang Bug Tracker because it has something to do with the Minecraft Launch Wrapper.

Here's the last line in the launcher_log.txt:

[0614/144307:INFO:GameCallbacks.cpp(178)] launcher/launcher (main) info Exception in thread "main" java.lang.ClassCastException: java.base/jdk.internal.loader.ClassLoaders$AppClassLoader cannot be cast to java.base/java.net.URLClassLoader[0614/144307:INFO:GameCallbacks.cpp(178)] launcher/launcher (main) info Exception in thread "main" java.lang.ClassCastException: java.base/jdk.internal.loader.ClassLoaders$AppClassLoader cannot be cast to java.base/java.net.URLClassLoader
at net.minecraft.launchwrapper.Launch.<init>(Launch.java:34)
at net.minecraft.launchwrapper.Launch.main(Launch.java:28)

Steps to reproduce

Install any modification for Minecraft (OptiFine for example)

 Note that the bug here is the Minecraft Launch Wrapper, which is a Minecraft library, and not the modification.