在空對象模式(Null Object Pattern)中,一個空對象取代 NULL 對象實例的檢查。Null 對象不是檢查空值,而是反應一個不做任何動作的關係。這樣的 Null 對象也可以在數據不可用的時候提供默認的行爲。
AbstractObject.m
classdef AbstractObject < handle
methods(Abstract)
operation(~);
end
end
RealObject.m
classdef RealObject < AbstractObject
properties
name
end
methods
function obj = RealObject(name)
obj.name = name;
end
function operation(obj)
disp("This is object " + obj.name + " operation.");
end
end
end
NullObject.m
classdef NullObject < AbstractObject
methods
function operation(~)
disp("This is NullObject");
end
end
end
ObjectFactory.m
classdef ObjectFactory < handle
properties(Constant)
names = ["matlab","pattern","design"];
end
methods(Static)
function res = getObject(name)
if(sum(ObjectFactory.names == name) > 0)
res = RealObject(name);
else
res = NullObject();
end
end
end
end
test.m
obj1 = ObjectFactory.getObject("matlab");
obj1.operation();
obj2 = ObjectFactory.getObject("null");
obj2.operation();
運行結果:
參考資料:
https://www.runoob.com/design-pattern/null-object-pattern.html