Constructor (object-oriented programming): Difference between revisions

Revision as of 10:20, 29 January 2019

Revision as of 10:19, 6 February 2019

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In [[class-based programming|class-based]] [[object-oriented programming]], a '''constructor''' (abbreviation: '''ctor''') is a special type of [[subroutine]] called to [[object creation|create an object]]. It prepares the new object for use, often accepting [[Parameter_(computer_programming)|arguments]] that the constructor uses to set required [[member variable]]s.

A constructordestructor resembles an [[method (computer science)|instance method]], but it differs from a method in that it has no explicit [[return type]], it is not implicitly [[inheritance (object-oriented programming)|inherited]] and it usually has different rules for scope modifiers. Constructors often have the same name as the declaring [[class (computer science)|class]]. They have the task of [[initialization (computing)|initializing]] the object's [[data member]]s and of establishing the [[Class invariant|invariant of the class]], failing if the invariant is invalid. A properly written constructor leaves the resulting [[object (computer science)|object]] in a ''valid'' state. [[Immutable object]]s must be initialized in a constructor.

Most languages allow [[method overloading|overloading]] the constructor in that there can be more than one constructor for a class, with differing parameters. Some languages take consideration of some special types of constructors. Constructors, which concretely use a single class to create objects and return a new instance of the class, are abstracted by [[Factory (object-oriented programming)|factories]], which also create objects but can do so in various ways, using multiple classes or different allocation schemes such as an [[object pool]].