Absent line number in Eclipse , Debugging disabled !

This is usually due to the compiler settings in Eclipse IDE , Windows -> preferences -> Java -> Compiler  -> "Add line number .. " should be checked . 


Another problem can be because JRE source is not mapped to the IDE . 

To ensure, you have the correct src.zip, do this:

Window->Preferences->Java->Installed JREs

Select your JRE and click “Edit”.

On the “Edit JRE” screen select the entry for rt.jar and click “Source Attachment” 

For me I used as JRE C:\Program Files\Java\jdk1.6.0_04\jre and with that my source attachment was in C:\Program Files\Java\jdk1.6.0_04\src.zip.

Hope this helps ..