http://www.kpdus.com/jad.html 에서 jad decompiler를 다운로드 받는다.
그리고, 아래의 순서로 jad를 쉽게 사용할 수 있다.

1. Download and unzip jadnt158.zip for Windows 9x/NT/2000 on Intel platform.
2. The directory where jad.exe is located should be put in your system environment variable PATH.
e.g.: PATH=..;C:\Tools\jad1.5.8;
3. To start using jad the following can be entered in a DOS window: jad
It displays a list of command line options and how to use jad. An overview of these options can be found in the table below.

Usage: jad [option(s)] <filename(s)>

Options	Description
-a	generate JVM instructions as comments (annotate)
-af	output fully qualified names when annotating
-b	generate redundant braces (braces)
-clear	clear all prefixes, including the default ones
-d <dir>	directory for output files
-dead	try to decompile dead parts of code (if there are any)
-dis	disassembler only (disassembler)
-f	generate fully qualified names (fullnames)
-ff	output fields before methods (fieldsfirst)
-i	print default initializers for fields (definits)
-l <num>	split strings into pieces of max <num> chars (splitstr)
-lnc	output original line numbers as comments (lnc)
-lradix <num>	display long integers using the specified radix
-nl	split strings on newline characters (splitstr)
-noconv	don't convert Java identifiers into valid ones (noconv)
-nocast	don't generate auxiliary casts
-noclass	don't convert .class operators
-nocode	don't generate the source code for methods
-noctor	suppress the empty constructors
-nodos	turn off check for class files written in DOS mode
-nofd	don't disambiguate fields with the same names (nofldis)
-noinner	turn off the support of inner classes
-nolvt	ignore Local Variable Table entries (nolvt)
-nonlb	don't insert a newline before opening brace (nonlb)
-o	overwrite output files without confirmation
-p	send all output to STDOUT (for piping)
-pa <pfx>	prefix for all packages in generated source files
-pc <pfx>	prefix for classes with numerical names (default: _cls)
-pe <pfx>	prefix for unused exception names (default: _ex)
-pf <pfx>	prefix for fields with numerical names (default: _fld)
-pi <num>	pack imports into one line using .* (packimports)
-pl <pfx>	prefix for locals with numerical names (default: _lcl)
-pm <pfx>	prefix for methods with numerical names (default: _mth)
-pp <pfx>	prefix for method parms with numerical names (default:_prm)
-pv <num>	pack fields with the same types into one line (packfields)
-r	restore package directory structure
-radix <num>	display integers using the specified radix (8, 10, or 16)
-s <ext>	output file extension (default: .jad)
-safe	generate additional casts to disambiguate methods/fields
-space	output space between keyword (if, while, etc) and expression
-stat	show the total number of processed classes/methods/fields
-t <num>	use <num> spaces for indentation (default: 4)
-t	use tabs instead of spaces for indentation
-v	show method names while decompiling
-8	convert Unicode strings into ANSI strings (ansi)
-&	redirect STDERR to STDOUT

4. To decompile a single file, just type:

jad -sjava HelloWorld.class

Jad creates the file HelloWorld.java

5. To decompile multiple class files, just type:

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

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

위내용은 http://www.mobilefish.com/developer/jad/jad.html 에서 발췌를 하였습니다.