A B737 FLT CREW HAVE AN NMAC WITH A NON XPONDERED CESSNA IN NCT CLASS E AIRSPACE.

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WHILE ON APCH TO SJC; WE WERE CLRED TO SJC VIA FINOR (SJC 118/16.8). AT APPROX 20 DME; WE CALLED THE FIELD IN SIGHT AND WERE CLRED VISUAL APCH TO RWY 30R. NORCAL (120.1) CALLED TFC (PRIMARY TARGET; ALT UNKNOWN) AT 12 O'CLOCK POS; 10 MI. WE LOOKED OUTSIDE BUT HAD NO CONTACT. WE CONTINUED SLOWING AND CONFIGURING FOR LNDG. AT 14 DME (INSIDE FINOR); NORCAL AGAIN CALLED PRIMARY TARGET AT 12 O'CLOCK POS; 2 MI. AT THAT MOMENT; I SAW A C172 IN A HARD R TURN (AVOIDANCE MANEUVER) ABOUT 400 FT L AND 200 FT BELOW OUR POS. I IMMEDIATELY LEVELED OFF (4500 FT) AND THE CESSNA DISAPPEARED BEHIND THE WING. HE APPEARED OK. MY LEVELOFF WAS NOT ABRUPT SINCE WE WERE SLOWING AND CONFIGURING WITH LESS THAN 500 FPM DSCNT. WE CONTINUED THE APCH TO AN UNEVENTFUL LNDG. WE RECEIVED NO TCASII WARNINGS. NORCAL WAS NOT IN RADIO CONTACT WITH THE CESSNA; NOR WAS THE CESSNA SQUAWKING XPONDER CODE. EVEN THOUGH WE WERE 'LOOKING OUTSIDE' FOR THE CONTACT; WE SAW HIM TOO LATE. THANK GOODNESS THE CESSNA SAW US OR WE MIGHT NOT BE HERE TO SUBMIT THIS RPT! TCASII IS A WONDERFUL THING; BUT EVERYONE HAS TO PLAY; IE; XPONDERS ON FOR IT TO HELP US.