jdk的major

J2SE 8 = 52,
J2SE 7 = 51,
J2SE 6.0 = 50,
J2SE 5.0 = 49,
JDK 1.4 = 48,
JDK 1.3 = 47,
JDK 1.2 = 46,
JDK 1.1 = 45

 http://en.wikipedia.org/wiki/Java_class_file

https://blogs.oracle.com/darcy/entry/bootclasspath_older_source

下次再报jvm的版本的时候就查一下是用哪个吧