Raise Exception using RAISE statement

PL/SQL block or subprogram should raise error message when undesirable or impossiable to finish processing. You can place RAISE statement for an exception within the scope of that exception.

SET SERVEROUTPUT ON
DECLARE
       out_of_stock  EXCEPTION;
       stock_in_hand   NUMBER(10)  := 100
BEGIN
       IF stock_in_hand < 1000 THEN
           RAISE out_of_stock;
       END IF;
EXCEPTION
     WHEN out_of_stock THEN
       DBMS_OUTPUT.PUT_LINE ('Stock in hand is less than 1000');
END;