Why is one d file compiled into two files object file & executable.

[Venkat Akkineni via Digitalmars-d-learn]

Hi

I am coming from Java. What is the purpose of an object file & 
why is it generated at compile time in addition to an executable. 
I know C generates an object file too, but I don't know what the 
use is.

Please point me to any detailed documentation u may have 
regarding object files.

Also does D have any facilities for dynamic code generation & 
compilation ?

Thankyou
Sincerely
Venkat