ORACLE PL/SQL 对象(object)学习笔记(三)

7、对象类型继承
 
对象类型实现允许我们创建一个基类型，或叫父类型，这种类型的属性或方法可以被另一个对象类型继承。然后可以创建一个子类型，或叫孩子类型，直接使用继承过来的属性或方法，或者用自己的属性和方法重写父类型的属性或方法。
 
INSTANTIABLE关键字表示我们可以从该类型中实例化或者创建对象实例。
FINAL关键字是指该对象类型下面不再有子类型，没有其他类型会继承该对象类型。
 
下面这个例子说明了继承关系，inventory_obj被book_obj继承。
 
CREATE OR REPLACE TYPE inventory_obj AS OBJECT (
item_id NUMBER (10),
num_in_stock NUMBER (10),
reorder_status VARCHAR2 (20 CHAR),
price NUMBER(10,2),
CONSTRUCTOR FUNCTION inventory_obj (
item_id IN NUMBER,
num_in_stock IN NUMBER,
price IN NUMBER
)
RETURN SELF AS RESULT,
MEMBER PROCEDURE print_inventory,
MEMBER PROCEDURE print_status,
MEMBER PROCEDURE print_price
)
INSTANTIABLE NOT FINAL;
/

CREATE OR REPLACE TYPE BODY inventory_obj
AS
CONSTRUCTOR FUNCTION inventory_obj (
item_id IN NUMBER,
num_in_stock IN NUMBER,
price IN NUMBER
)
RETURN SELF AS RESULT
IS
BEGIN
SELF.item_id := item_id;
SELF.num_in_stock := num_in_stock;
SELF.price := price;
RETURN;
END;
MEMBER PROCEDURE print_inventory
IS
BEGIN
DBMS_OUTPUT.put_line ('INVENTORY FOR BOOKSTORE1');
DBMS_OUTPUT.put_line ('========================');
DBMS_OUTPUT.put_line ( 'Item number '
|| SELF.item_id
|| ' has '
|| SELF.num_in_stock
|| ' in stock'
);
END print_inventory;
MEMBER PROCEDURE print_status
IS
v_status VARCHAR2 (20);
BEGIN
IF SELF.num_in_stock > 0
THEN
v_status := 'IN STOCK';
ELSE
v_status := 'OUT O