How do i edit java code whilst the app is running like notch does in eclipse? [duplicate]

I would like to debug the whole flow of a java program line by line and I am using eclipse how can I do that?

There are multiple steps required to debug a java program in eclipse such as:

1. Setting breakpoints
2. Starting the debugger
3. controlling the program execution. For line by line use F6 and F5 to step into a method
4. Evaluating variables etc

Putting everthing here will make the answer too long. I advice you to follow this tutorial :

http://www.vogella.com/articles/EclipseDebugging/article.html

Create a break point in the first line of your main method then using F5 (step into) to walk through it.

BTW, such questions are all over the web. To be a good programmer, use google wisely.