Initialization event flow

Hi Experts,

I was just practicing and came to know that:

PARAMETERS P_MATNR TYPE MATNR DEFAULT 'A112233'.

INITIALIZATION.
WRITE 'INITIALIZATION'.

START-OF-SELECTION.
WRITE 'START OF SELECTION'.

END-OF-SELECTION.
WRITE: 'END OF SELECTION'.

does not write INITIALIZATION.

But without PARAMETERS statement it writes.

can anyone explain me why it is so.

Thanks,

Vibhor