内容：定义了一个创建对象的接口，但由子类决定要实例化的类是哪一个。工厂方法让类把实例化推迟到子类。
简单来说，工厂方法模式能够封装具体的类型的实例化。
结构：
image
Product:所有产品都必须实现这个共同的接口，这样一来，使用这些产品的类就可以引用这个接口，而不是具体类。
ConcreteCreator:负责创建一个或者多个具体产品，只有concrete creator类知道如何创建这些产品。同时，它实现了factory method，以实际制造出产品。
Creator: 是一个抽象类，它实现了所有操作产品的方法，但不实现工厂方法。其所有的子类都必须实现这个抽象的factorymethod()方法。
实例程序，首先给出类图：
image
注意：创建类和产品类是平行的，因为他们都是抽象类，而抽象类都有许多具体的子类，每个子类都有自己特定的实现。
测试程序如下：
REPORT ZBOBO_DP_004_RE .
*Factory method pattern used interface and class
include zbobo_dp_004_if_cl.
*This data used to create two type of concrete creator
data:
ny_ref type ref to pizzastore,
chi_ref type ref to pizzastore.
*The different pizza have the same interface
data:
pz_ref type ref to pizza.
start-of-selection.
* Create two different pizzastore
create object ny_ref type ny. "For NY
create object chi_ref type chi."For Chi
* Book NY store's pizza
call method ny_ref->orderpizza
exporting pz_name1 = 'cheese'
receiving pz = pz_ref.
* Get the pizza's name
data: ls type string.
call method pz_ref->getname
receiving na = ls.
write: / 'Ethan ordered a:',ls.
skip.
* Book Chi store's pizza
call method chi_ref->orderpizza
exporting pz_name1 = 'cheese'
receiving pz = pz_ref.
* Get the pizza's name
call method pz_ref->getname
receiving na = ls.
write: / 'Joel ordered a:',ls.
**抽象产品类：**
*----------------------------------------------------------------------*
* INCLUDE ZBOBO_DP_004_IF_CL *
*----------------------------------------------------------------------*
*Declare product class
class pizza definition abstract.
public section.
* Define instance variants
data:
name type string,
dough type string,
sauce type string.
data:
begin of rtab,
str type string,
end of rtab,
itab like table of rtab.
* Methods which will be inherited by subclass
methods:
* Prepare pizza
prepare,
* Bake pizza
bake,
* Cut pizza
cut,
* Boxing pizza
box,
* Getter method to get pizza name
getname
returning value(na) type string.
endclass.
*Implement the pizza class
class pizza implementation.
method prepare.
write:
/ 'Preparing:', name,
/ 'Tossing dough....',
/ 'Adding sauce....',
/ 'Adding toppings:'.
loop at itab into rtab.
write: / rtab-str.
endloop.
endmethod.
method bake.
write: / 'Bake for 25 minutes at 350'.
endmethod.
method cut.
write: / 'Cutting the pizza into diagonal slices'.
endmethod.
method box.
write: / 'place pizza in official PizzaStore box'.
endmethod.
method getname.
na = name.
endmethod.
endclass.
**工厂类：**
*Delare plant method class
*We can now define plant class,note that it is in the same leve as produ
class pizzastore definition abstract.
public section.
methods:
* This method is used to order the concrete product
orderpizza
importing pz_name1 type string
returning value(pz) type ref to pizza.
protected section.
methods:
* This method seems like a factory
* Because this method is abstract, the subclass must instantiate thi
* This method must have a return value, which is the concrete produc
createpizza abstract
importing pz_name2 type string
returning value(pz) type ref to pizza.
endclass.
class pizzastore implementation.
method orderpizza.
data: pz_ref type ref to pizza.
* This is the key part of factory method pattern
* We use factory method to create concrete product
call method createpizza
exporting pz_name2 = pz_name1
receiving pz = pz_ref.
* Other methods
call method:
pz_ref->prepare,
pz_ref->bake,
pz_ref->cut,
pz_ref->box.
* Return the concrete product which have been created
pz = pz_ref.
endmethod.
endclass.
**具体产品类：**
*OK, now we can concrete product
class nystylepizza1 definition
inheriting from pizza.
public section.
methods:
constructor.
endclass.
class nystylepizza1 implementation.
method constructor.
call method super->constructor.
name = 'NY style Sauce and Cheese Pizza'.
dough = 'Thin Crust Dough'.
sauce = 'Marinara Sauce'.
rtab-str = 'Grated Reggiano Cheese'.
append rtab to itab.
endmethod.
endclass.
class chistylepizza1 definition
inheriting from pizza.
public section.
methods:
constructor,
cut redefinition.
endclass.
class chistylepizza1 implementation.
method constructor.
call method super->constructor.
name = 'Chicago Style Deep Dish Cheese Pizza'.
dough = 'Extra Thick Crust Dough'.
sauce = 'Plum Tomato Sauce'.
rtab-str = 'Shredded Mozzarella Cheese'.
append rtab to itab.
endmethod.
method cut.
write: / 'Cutting the pizza into square slices'.
endmethod.
endclass.
**具体创建类：**
*Now we can define the concrete creator
class ny definition inheriting from pizzastore.
protected section.
methods:
createpizza redefinition.
endclass.
class ny implementation.
method createpizza.
case pz_name2.
when 'cheese'.
create object pz type nystylepizza1.
when 'vegie'.
when 'clam'.
when 'pepperoni'.
endcase.
endmethod.
endclass.
class chi definition inheriting from pizzastore.
protected section.
methods:
createpizza redefinition.
endclass.
class chi implementation.
method createpizza.
case pz_name2.
when 'cheese'.
create object pz type chistylepizza1.
when 'vegie'.
when 'clam'.
when 'pepperoni'.
endcase.
endmethod.
endclass.
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