When changing Java versions, you may have some problems.
Just delete the former .class files, and the former .jar files created with the previous version of Java, before re-creating them.
Typically, when compiling a .java file, you will end up with an error like this:
$ javac -Xlint MyTestClass.java
.java:28: error while writing
.class (Operation not supported)
The re-creation won't work: the formerly created files must be deleted.