1. Compile a class file in advance
2. Use to open the class file
3. Only look at the first line of data, the first 8 bytes CA FE BA BE are fixed, the next 4 bytes 00 00 are the minor version number, and the 4 bytes 00 33 after the minor version number are the jdk version number , as I am using jdk1.7 here
The corresponding relationship of the jdk version number is as follows:
The version number corresponds to the decimal jdk version number
