Has been compiled by a more recent version of the Java Runtime (class file version 60.0)

Java version names in error messages:
49 = Java 5
50 = Java 6
51 = Java 7
52 = Java 8		(or 1.8)
53 = Java 9
54 = Java 10
55 = Java 11
56 = Java 12
57 = Java 13
58 = Java 14

Solutions:
1. Update your JRE to the same version as your JDK
If done manually in cmd:
2. javac --release 8 yourClass.java			(of course insert wanted version number here)
3. javac -source 1.8 -target 1.8  *.java	(Shows warning)