組合模式(Composite),將對象組合成樹形結構以表示“部分-整體”的層次結構,組合模式使得用戶對單個對象和組合對象的使用具有一致性。組合模式的目的是讓客戶端不再區分操作的是組合對象(Composite)還是葉子對象(Leaf),而是以一個統一的方式來操作。實現這個目標的關鍵之處,是設計一個抽象的組件類,讓它可以代表組合對象和葉子對象。這樣一來,客戶端就不用區分到底是組合對象還是葉子對象了,只需要全部當成組件對象進行統一的操作就可以了。計算機系統的文件夾相當於組合模式的Composite,文件相當於組合模式的Leaf。本文按照下面的類圖,用Matlab代碼實現組合模式。
Component.m
classdef Component < handle & matlab.mixin.Heterogeneous
properties(Access = protected)
name
end
methods
function obj = Component(name)
obj.name = name;
end
end
methods(Abstract)
Add(~,~);
Remove(~,~);
Display(~,~);
end
methods(Sealed)
function res = eq(obj1,obj2)
res = eq@handle(obj1,obj2);
end
function res = ne(obj1,obj2)
res = ne@handle(obj1,obj2);
end
end
end
Composite.m
classdef Composite < Component
properties(Access = private)
children = Component.empty();
end
methods
function obj = Composite(name)
obj = obj@Component(name);
end
function Add(obj,c)
obj.children(end + 1)=c;
end
function Remove(obj,c)
index = [obj.children] ~= c;
obj.children = obj.children(index);
end
function Display(obj,depth)
temp = "";
for i = 1:depth
temp = temp + "-";
end
disp(temp + obj.name);
for i = 1:length(obj.children)
obj.children(i).Display(depth + 1);
end
end
end
end
Leaf.m
classdef Leaf < Component
methods
function obj = Leaf(name)
obj = obj@Component(name);
end
function Add(~,~)
end
function Remove(~,~)
end
function Display(obj,depth)
temp = "";
for i = 1:depth
temp = temp + "-";
end
disp(temp + obj.name);
end
end
end
測試代碼:
root = Composite("Composite root");
compX = Composite("Composite X");
root.Add(Leaf("Leaf A"));
root.Add(compX);
root.Add(Leaf("Leaf B"));
compX.Add(Leaf("Leaf XA"));
compX.Add(Leaf("Leaf XB"));
compXY = Composite("Composite XY");
compX.Add(compXY);
leafXYA = Leaf("Leaf XYA");
compXY.Add(leafXYA);
compXY.Add(Leaf("Leaf XYB"));
compXY.Remove(leafXYA);
root.Display(0);
運行結果: