Decompile all the class files in a directory using JAD

Download JAD from
http://www.varaneckas.com/jad

place the jad file in C:\ drive
Add environment variable c:\ to %path%
go to the directory where class files exists using command prompt
run the below commands as required.

jad -o -d -r . -s java **/*.class (Recursive Decompilation of all files within a directory)
jad -o -d . -s java X.class (to decompile a single class)
jad -o -d . -s java *.class