处理报错：java/lang/NoClassDefFoundError: java/lang/Object
操作系统环境：CentOS6.0 2.6.32-220.el6.x86_64
JDK版本环境：jdk1.5.0_22
操作系统原来安装的是jdk1.6,后来开发人员要求java程序使用jdk1.5版本的。帮开发下载JDK1.5,
安装完JDK ，设定环境变量后出现这个错误：

1. [root@fztest97 lib]# javac
2. Error occurred during initialization of VM
3. java/lang/NoClassDefFoundError: java/lang/Object
4. [root@fztest97 lib]# java
5. Error occurred during initialization of VM
6. java/lang/NoClassDefFoundError: java/lang/Object

首先要确认的是环境变量的设置是否正确，其次，需要确认的就是lib和jre/lib文件夹中的rt和tools是否是打包后的形式，如果发现rt.pack 和 tools.pack 那么多半问题就出在这里。
解决方法也很简单，只要将相应文件解压成rt.jar 和 tools.jar，可以使用bin里面的unpack200工具，
如：unpack200 rt.pack rt.jar
/apps/usr/java/jdk1.5.0_22/lib/tools.pack 转为 tools.jar
/apps/usr/java/jdk1.5.0_22/jre/lib/rt.pack 转为 rt.jar
执行如下操作命令：

1. [root@fztest97 ]# cd /apps/usr/java/jdk1.5.0_22/lib/
2. [root@fztest97 lib]# unpack200 tools.pack tools.jar
3. [root@fztest97 lib]# ls
4. dt.jar ir.idl jconsole.jar orb.idl sa-jdi.jar tools.jar tools.pack
5. [root@fztest97 lib]# cd /apps/usr/java/jdk1.5.0_22/jre/lib
6. [root@fztest97 lib]# unpack200 rt.pack rt.jar
7. [root@fztest97 lib]# ll rt.*
8. -rw-r--r--. 1 root root 40232487 May 23 19:23 rt.jar
9. -rw-r--r--. 1 root root 12960918 May 23 19:07 rt.pack

再次执行如下命令，进行验证：

1. [root@fztest97 lib]# java -version
2. java version "1.5.0_22"
3. Java(TM) 2 Runtime Environment, Standard Edition (build 1.5.0_22-b03)
4. Java HotSpot(TM) 64-Bit Server VM (build 1.5.0_22-b03, mixed mode)
5. [root@fztest97 lib]# javac
6. Usage: javac <options> <source files>
7. where possible options include:
8. -g Generate all debugging info
9. -g:none Generate no debugging info
10. -g:{lines,vars,source} Generate only some debugging info
11. -nowarn Generate no warnings
12. -verbose Output messages about what the compiler is doing
13. -deprecation Output source locations where deprecated APIs are used
14. -classpath <path> Specify where to find user class files
15. -cp <path> Specify where to find user class files
16. -sourcepath <path> Specify where to find input source files
17. -bootclasspath <path> Override location of bootstrap class files
18. -extdirs <dirs> Override location of installed extensions
19. -endorseddirs <dirs> Override location of endorsed standards path
20. -d <directory> Specify where to place generated class files
21. -encoding <encoding> Specify character encoding used by source files
22. -source <release> Provide source compatibility with specified release
23. -target <release> Generate class files for specific VM version
24. -version Version information
25. -help Print a synopsis of standard options
26. -X Print a synopsis of nonstandard options
27. -J<flag> Pass <flag> directly to the runtime system

到此为止，JDK1.5安装配置成功。