Constructor (object-oriented programming): Difference between revisions

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Revision as of 21:19, 12 November 2006

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In [[object-oriented programming]], a '''constructor''' (sometimes shorted to '''ctor''') in a class is a special block of statements called when an object is declared or explicitally constructed trough the new keyword, depending by the language. A constructor is similar to [[method (computer science)|methodclass methods]], (function)but calledit whenis annot objecta isspecial declaredkind of method: andit never has a return type, it's not inherited, has different rules for modifiers. Constructors are special [[methodblock (computerof science)|instance methods]]statements that are called automatically upon the creation of an [[object (computer science)|object]] (instance of a class). They are often distinguished by having the same name as the [[class (computer science)|class]] of the object they're associated with. Its main purpose is to pre-define the object's [[data member]]s and to establish the [[invariant (computer science)|invariant]] of the class, failing if the invariant isn't valid. A properly written constructor will leave the [[object (computer science)|object]] in a 'valid' state.

=== [[Java programming language|Java]] ===

Some of the differences between Java methods and constructors:

*Constructors never have a return type.

*Constructors can't be overridden, nor they are inherited

*Constructors shouldn't call other overridable methods

*Constructors can't be synchronized

*Constructors are always executed by the same thread

*Constructors can't be final

*Constructors can't be abstract

==== Example ====

public class Example

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==References==

* [[Bjarne Stroustrup]]: ''The C++ Programming Language'', Addison-Wesley, ISBN 0-201-70073-5

* [[James Gosling]]: ''The Java Programming Language'', Addison-Wesley, ISBN 0-321-34980-6

[[Category:Programming constructs]]