ALV TREE DOUBT

Hi frnds,

i was going thru "BCALV_TREE_SIMPLE_DEMO", i got a doubt that

" class cl_gui_column_tree definition load.

class cl_gui_cfw definition load."

what is the purpose of "load" and can anyone please explain me the flow of

"BCALV_TREE_SIMPLE_DEMO" program.

Thanking u all.

satya