Hi!
I had similar problems. Did you have Java 7 installed, before you installed Java 8? In that case, did you changed the paths? Because it seems, that Pyjnius still uses Java 7. It needs the JDK_HOME, JAVA_HOME and PATH variables to be set up to the proper places. You can check, which version Pyjnius uses with the following, short Python code:
from pyjnius import autoclass
System = autoclass('java.lang.System')
print("My Jave version is: {}.".format(System.getProperty('java.version')
Cheers!
Csega