下面定义一个具体的观察者：current_condition_display
*Concrete observers
*Display current weather data
class current_condition_display definition.
public section.
* Implement two interfaces, observer and display_element
interfaces:
observer,
display_element.
methods:
* Get the initial concrete subject object
constructor
importing wd type ref to subject.
private section.
data:
tem type f,
hum type f.
* Concrete subject
data w_data type ref to weather_data.
endclass.
class current_condition_display implementation.
* Update data
method observer~update.
me->tem = temp.
me->hum = hum.
call method display_element~display.
endmethod.
* Display data
method display_element~display.
write: / 'Current conditions:'.
write: / me->tem decimals 2 exponent 0,
'F degrees.'.
write: / me->hum decimals 2 exponent 0,
'% humidity.'.
endmethod.
method constructor.
* Widening cast because wd's type which import is interface subject
* and the me->w_data's type is weather_data
* and weather data is more specialized than interface subject
me->w_data ?= wd.
* Register current condition observer to subject
call method w_data->subject~register_observer
exporting o = me.
endmethod.
endclass.
*Display current weather data
class current_condition_display definition.
public section.
* Implement two interfaces, observer and display_element
interfaces:
observer,
display_element.
methods:
* Get the initial concrete subject object
constructor
importing wd type ref to subject.
private section.
data:
tem type f,
hum type f.
* Concrete subject
data w_data type ref to weather_data.
endclass.
class current_condition_display implementation.
* Update data
method observer~update.
me->tem = temp.
me->hum = hum.
call method display_element~display.
endmethod.
* Display data
method display_element~display.
write: / 'Current conditions:'.
write: / me->tem decimals 2 exponent 0,
'F degrees.'.
write: / me->hum decimals 2 exponent 0,
'% humidity.'.
endmethod.
method constructor.
* Widening cast because wd's type which import is interface subject
* and the me->w_data's type is weather_data
* and weather data is more specialized than interface subject
me->w_data ?= wd.
* Register current condition observer to subject
call method w_data->subject~register_observer
exporting o = me.
endmethod.
endclass.
