ABAP CLEAR VS REFRESH

REFRESH and CLEAR are the various methods for initializing Internal Tables.
examples:
CLEAR <itab>.
If <itab> is not having header line, this will clear the entire contents.
CLEAR <itab>.
If <itab> is having header line, this statement will just clear the contents of header line.
CLEAR <itab>[]
If <itab> has header line, this will clear the body contents ( excluding header line)
REFRESH <itab>.
This statement will cause the body content to be cleared. But memory allotted to the table will remain as it is.. Then u have to use
FREE<itab> to free the memory.