composition组合和aggregation聚合之间的区别 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.
参考:http://en.wikipedia.org/wiki/Object_composition
简单来说:
composition组合,是实心菱形,个体不可以脱离整体存在,生命周期一致
aggregation聚合,是空心菱形,个体生命周期跟整体的可以不一致
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