1）首先，你必須安裝有JDK，並且配置好了環境變數。。。至於配置，不多說，自己google。然後在cmd進入你的jfreechart-1.0.14-demo.jar所在資料夾，輸入
jar -xvf jfreechart-1.0.14-demo.jar
如果對-xvf不懂得可以用 輸入jar檢視
2）下載jad的軟體，到http://www.varaneckas.com/jad下載一個，解壓縮jad.exe 複製到jdk的bin資料夾下面，輸入

jad -o -r -sjava -dsrc demo/**/*.class

This command decompiles all .class files located in all subdirectories of 'demo' and creates output files in subdirectories of 'src' according to package names of classes. For example, if file 'demo/a/b/c.class' contains class 'c' from package 'a.b', then output file will have a name 'src/a/b/c.java'.

Note the use of the "two stars" wildcard ('**') in the previous command. It is handled by Jad rather than the command shell, so on UNIX the last argument should be single-quoted:

jad -o -r -sjava -dsrc 'demo/**/*.class

然後，在src資料夾下面，你會有意想不到的驚喜。。