JDK自带javap命令反编译class文件和Jad反编译class文件（推荐使用jad）

public class JavaPTest {
    String string = new String("学") + new String("Java");
}

C:\Users\Administrator>javap
用法: javap <options> <classes>
其中, 可能的选项包括:
  -help  --help  -?        输出此用法消息
  -version                 版本信息
  -v  -verbose             输出附加信息
  -l                       输出行号和本地变量表
  -public                  仅显示公共类和成员
  -protected               显示受保护的/公共类和成员
  -package                 显示程序包/受保护的/公共类
                           和成员 (默认)
  -p  -private             显示所有类和成员
  -c                       对代码进行反汇编
  -s                       输出内部类型签名
  -sysinfo                 显示正在处理的类的
                           系统信息 (路径, 大小, 日期, MD5 散列)
  -constants               显示最终常量
  -classpath <path>        指定查找用户类文件的位置
  -cp <path>               指定查找用户类文件的位置

C:\Users\Administrator>jad
Jad v1.5.8g. Copyright 2001 Pavel Kouznetsov (jad@kpdus.com).
Usage:    jad [option(s)] <filename(s)>
Options: -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

// Decompiled by Jad v1.5.8g. Copyright 2001 Pavel Kouznetsov.
// Jad home page: http://www.kpdus.com/jad.html
// Decompiler options: packimports(3) 
// Source File Name:   JavaPTest.java
package com.wang.test.demo.putong;
public class JavaPTest
{
    public JavaPTest()
    {
        string = (new StringBuilder()).append(new String("wang"))
        .append(new String("zhjen")).toString();
    }
    String string;
}