how can desing debug tool?

I understand load class method, sample :

http://www.google.com.tw/search?q=cache:mSauMkxLHqAJ:jguru.com/faq/view.jsp%3FEID%3D463990+VirtualMachine+resume+import&hl=zh-TW

how to design command ~~ like step , show code .... hava any easy sample ,

java jpda demo code is too hard for me , Thanks. Regard.

[330 byte] By [is_me] at [2007-9-30 17:55:19]
# 1
Why not use freely available debuggers which are integrated into IDEs like NetBeans or Eclipse.What do you hope to achieve with your own debugger?
Peter-Lawrey at 2007-7-6 14:31:28 > top of Java-index,Archived Forums,Debugging Tools and Techniques...
# 2

NetBeans and Eclipse are good IDE tools, I just want to learn to desing debug tool, so I need som help.

The demo code of C:\j2sdk1.4.2_05\demo\jpda\example , I run it, but hava some trouble,

I choice file and rue it , it always say :

Disconnected from VM

Starting child.

Connected to VM

Running ...

VM started

Exception: java.lang.ClassNotFoundException and [ Source code is not available ] , @@||| Why ?

is_me at 2007-7-6 14:31:28 > top of Java-index,Archived Forums,Debugging Tools and Techniques...