The difference between aggregation and composition in UML

summary ：
The combination is national ruin , Can't exist alone ;
Convergence is the bankruptcy of training institutions , The teacher runs , It doesn't have much impact on teachers ;

explain ：

all the time , Yes UML Things are always ambiguous , For aggregation and composition in class diagrams , Know the difference between the two , But after a period of time, I can't tell which is which , alas , It's mainly because I didn't learn Chinese good , ha-ha ！

Actually , For aggregation and composition , If you change it to English , That makes sense ： Aggregation is “has-a”, Combination is “contains-a”.

Aggregation is a hollow diamond ; The combination is a solid diamond （ This is easier to understand , Solid must be more solid than hollow , ha-ha ）.

Extract a passage ：

The difference between aggregation and combination is ： The aggregation relationship is “has-a” Relationship , The combination is “contains-a” Relationship ; The aggregation relationship means that the relationship between the whole and the part is relatively weak , And the combination is stronger ; The object that represents part of things in the aggregation relationship has nothing to do with the lifetime of the object that represents the aggregation , Once you delete an aggregate object, you don't necessarily delete the object that represents part of it . Once the combined object is deleted in the combination , At the same time, the objects representing some things are deleted .

We use simple examples to illustrate the difference between aggregation and composition .“ the country is defeated and the home lost ”, The country is destroyed , Naturally, there is no home ,“ countries ” and “ home ” Obviously, it is also a combination relationship . On the contrary , The relationship between the computer and its peripherals is aggregation , Because the relationship between them is relatively loose , The computer is gone , Peripherals can also exist independently , It can also be connected to other computers . In an aggregate relationship , Parts can exist independently of aggregation , Partial ownership can also be shared by several aggregations , For example, printers can be shared by colleagues in the office .

Java Programming ideas in Zhongyuan ： Use existing classes Synthesize new classes , So this concept is called combination , If the combination is dynamic , Then call it aggregation .