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在空对象模式(Null Object Pattern)中,一个空对象取代 NULL 对象实例的检查。Null 对象不是检查空值,而是反应一个不做任何动作的关系。这样的 Null 对象也可以在数据不可用的时候提供默认的行为。
AbstractObject.m
- classdef AbstractObject < handle
- methods(Abstract)
- operation(~);
- end
- end
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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
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NullObject.m
- classdef NullObject < AbstractObject
- methods
- function operation(~)
- disp("This is NullObject");
- end
- end
- end
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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
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test.m
- obj1 = ObjectFactory.getObject("matlab");
- obj1.operation();
- obj2 = ObjectFactory.getObject("null");
- obj2.operation();
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