Yes, to follow up on
OliverA's question above, are you double clicking on the JAR file to run it?
If the answer to my question is Yes.... I had a similar problem during an automatic Java update and I have disabled automatic updates ever since....
Come to find out that there was NOTHING wrong with the JAR file. The problem was the Windows association of the jar file with the java runtime. I can't remember how I fixed it, but once I did, the jar file could be run with a double click. I'll try to find out what I did but in the meantime I suggest you research how the Java8 JRE installer does this association during installation/updates. During the update, that association probably got screwed up.... not uncommon with updates as you probably know
Here's something I found in a quick Google search. Have not read it but it's worth looking at:
While trying to run a .jar file (Optifine installer for Minecraft), I accidentally thought that I could use the OpenJDK package that comes with Android Studio to run it. However, I was wrong, and n...
superuser.com
BTW.. if you want to confirm that this is actually the issue, open a command prompt and go to the folder that has the jar file you want to run. Enter:
java -version
[confirm the correct version installed]
java -jar myprogram.jar
If it runs, my theory is correct.