Aggregation vs Composition

Ahetuki Neti

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posted 21 years ago

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What is the difference between aggregation and composition?

Ahetuki, the Constant.

Lasse Koskela

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posted 21 years ago

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Composition is really a strong form of aggregation.

Composed objects have only one owner

Composed objects cannot exist independent of their owner (components live and die with their owner)

Aggregations may form "part of" the aggregate, but may not be essential to it. They also may also exist independent of the aggregate.

[ May 30, 2003: Message edited by: Lasse Koskela ]

Author of Test Driven (2007) and Effective Unit Testing (2013) [Blog] [HowToAskQuestionsOnJavaRanch]

Ilja Preuss

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posted 21 years ago

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With other words: Composition adds a responsibility for controlling the lifetime of the part.
In garbage collected languages like Java, there isn't much use for composition, in fact...

The soul is dyed the color of its thoughts. Think only on those things that are in line with your principles and can bear the light of day. The content of your character is your choice. Day by day, what you do is who you become. Your integrity is your destiny - it is the light that guides your way. - Heraclitus

With a little knowledge, a cast iron skillet is non-stick and lasts a lifetime.