Keywords: UML
Analyze the definitions and relationships of association, aggregation, and combination in a UML class diagram.@ Author: ZJ 06-11-27http: // zhangjunhd.blog.51cto.com/
1. Association)Most of the associations between classes are used to indicate that the variable instance holds a reference to other objects. Phone has a reference to the button.
2. Aggregation)Aggregation is a special form of association, which means a whole/part relationship. A whole cannot be a part of itself. Therefore, an instance cannot form an aggregation loop. A single object cannot be its own aggregation, two objects cannot be aggregated, and three objects cannot form an aggregation ring. It is an illegal aggregation cycle between instances:
3. Composition)Combination is a special form of aggregation. UML defines a combination: ① like aggregation, the instance cannot have loops. ② An owned instance cannot have two owners at the same time. ③ The owner is responsible for managing the lifecycle of the combined object. If the owner is destroyed, the owner must also be destroyed together. If the owner is copied, the owner must also be copied together. Based on this, you can use a combination to describe deep copy. Invalid combination:
4. References(1) Robert Martin, UML for Java programmers, 2004
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