Package
- Encapsulate variables and functions that are similar in business into structures (classes)
- Reduce the number of directly managed members, facilitating large-scale development
inherit
- Extract the common part to the parent class to reduce duplication of code
Polymorphism
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A parent category has many different specific sub-category forms
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Commonality: dispatch subclass instances by calling the parent class method
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Personality: different subclasses have different abstractions for the concrete realization of the parent class method
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The parent interface only defines methods, not specific implementations