Editing Class invariant (section)

{{short description|Unchanging property for all objects of a class}}
{{about|the computer programming concept|the mathematical concept|Equivalence class|and|Invariant (mathematics)}}
{{more citations needed|date=August 2010}}

In [[computer programming]], specifically [[object-oriented programming]], a '''class invariant''' (or '''type invariant''') is an [[invariant (computer science)|invariant]] used for constraining [[object (computer science)|objects]] of a [[class (computer science)|class]]. [[Method (computer science)|Methods]] of the class should preserve the invariant. The class invariant constrains the state stored in the object.

Class invariants are established during [[Constructor (object-oriented programming)|construction]] and constantly maintained between calls to public methods. Code within functions may break invariants as long as the invariants are restored before a public function ends. With [[Concurrent computing|concurrency]], maintaining the invariant in methods typically requires a critical section to be established by locking the state using a [[mutex]].

An '''object invariant''', or '''representation invariant''', is a computer programming construct consisting of a set of invariant properties that remain uncompromised regardless of the state of the object. This ensures that the object will always meet predefined conditions, and that methods may, therefore, always [[Reference (computer science)|reference]] the object without the risk of making inaccurate presumptions. Defining class invariants can help programmers and testers to catch more bugs during [[software testing]].