JDK 8 = 52,
JDK 7 = 51,JDK 6.0 = 50,JDK 5.0 = 49,JDK 1.4 = 48,JDK 1.3 = 47,JDK 1.2 = 46,JDK 1.1 = 45
jdk版本号对应major version号
原文：http://www.cnblogs.com/luyang08/p/6358639.html
