Stage 1 · Lesson 2 of 8
Encapsulation and invariants
means hiding an object's internal state behind a small set of methods. An is a rule that must always be true for the object, such as a balance never going negative or an order total always matching its lines. If the only way to change the balance is a deposit method that rejects bad amounts, the rule holds everywhere, forever.
You can also change how the data is stored without touching any caller. Make fields private by default and expose behaviour, such as withdraw, rather than raw data, such as setBalance.
Common trapgenerating a getter and a setter for every field out of habit, which makes the field public in all but name and leaves the rules unprotected.
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Resources for this stage
Start with· follow one of these
- CoursePaidGrokking the Object Oriented Design Interview
Design Gurus · Intermediate · Subscription
Its opening chapters teach the four OOP ideas applied inside real designs, with UML and running code
- CourseFreeMIT 6.102: Software Construction
MIT · Intermediate
Free MIT readings: Abstract Data Types, Rep Invariants and Interfaces and Subtyping are this stage at university depth