composition組合和aggregation彙總之間的區別 difference

In UML, composition is depicted as a filled diamond and a solid line. It always implies a multiplicity of 1 or 0..1, as no more than one object at a time can have lifetime responsibility for another object.

The more general form, aggregation, is depicted as an unfilled diamond and a solid line. The image below shows both composition and aggregation. The C++ code below shows what the source code is likely to look like.

 

參考：http://en.wikipedia.org/wiki/Object_composition

 

簡單來說：

composition組合，是實心菱形，個體不可以脫離整體存在，生命週期一致

aggregation彙總，是空心菱形，個體生命週期跟整體的可以不一致