The version number shown describes the version of the JRE the class file is compatible with.

 

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


javac -target 1.4HelloWorld.java