Minecraft FTB Client – OSX Java Issue

So the other day I had a pretty big hankering to play some Minecraft. I downloaded Feed the Beast (FTB) and a modpack I liked that reminded me of what I used to play on Tekkit. Go to launch, and…. problems. The client wouldn’t work.

feed the beast Exception in thread "main" java.lang.ClassCastException: java.base/jdk.internal.loader.ClassLoaders$AppClassLoader cannot be cast to java.base/java.net.URLClassLoader

What I realized is that there was a problem with Java on OSX- in this case, it was too new to properly launch FTB. Rather than downgrading my Java version, which isn’t good for obvious reasons, I decided to download a standalone older version and then point the FTB launcher to it.

In this case, downloading Java SE Runtime Environment 8u212 did the trick. We are looking for the .tar.gz file and not the .dmg, which will open the full GUI automated installer. Once downloaded, unzip or un tar the tar.gz file.

Now we need to locate the Java bin file. In my case, it was located inside the unzipped tar.gz file here:

jre1.8.0_212.jre > Contents > Home > bin > java

Open the FTB client. Under the profile selector, click on “Edit Profile.” Under Java Settings (Advanced), check the “Executable” box and use the location of the Java bin file we just downloaded and found in the last step.


Make sure both the “Executable” and the “JVM Arguments” boxes are checked. Hit “Save Profile” and you should be good to go!