JavaBeans: Difference between revisions

Revision as of 16:56, 8 July 2021

Latest revision as of 09:58, 3 January 2025

(20 intermediate revisions by 18 users not shown)

Line 1:

{{Short description|Computing technology developer by Sun Microsystems}}

{{Distinguish|Enterprise JavaBeans}}

{{multiple issues|

{{refimprovemore citations needed|date=June 2016}}

{{manualhow-to|date=October 2012}}

}}

In computing based on the [[Java (programming language)|Java]] Platform, '''JavaBeans''' is a technology developed by [[Sun Microsystems]] and released in 1996, as part of [[Java Development Kit|JDK]] 1.1.

In computing based on the Java Platform, '''JavaBeans''' are classes that encapsulate many [[Object (computer science)|objects]] into a single object (the bean). They are [[Serialization|serializable]], have a [[nullary constructor|zero-argument constructor]], and allow access to properties using [[Mutator method|getter and setter methods]]. The name "Bean" was given to encompass this standard, which aims to create [[Code reuse|reusable]] [[Component-based software engineering|software components]] for [[Java (programming language)|Java]].

The 'beans' of JavaBeans are classes that encapsulate one or more [[Object (computer science)|objects]] into a single standardized object (the bean). This standardization allows the beans to be handled in a more generic fashion, allowing easier [[code reuse]] and [[Type introspection|introspection]]. This in turn allows the beans to be treated as [[Component-based software engineering|software components]], and to be manipulated visually by [[Integrated development environment|editors and IDEs]] without needing any initial configuration, or to know any internal implementation details.

It is a reusable software component written in Java that can be manipulated visually in an application builder tool.

As part of the standardization, all beans must be [[Serialization|serializable]], have a [[nullary constructor|zero-argument constructor]], and allow access to properties using [[Mutator method|getter and setter methods]].

==Features==

;Introspection

:Introspection is a process of analyzing a Bean to determine its capabilities. This is an essential feature of the Java Beans APIspecification because it allows another application, such as a design tool, to obtain information about a component.

;Properties

:A property is a subset of a Bean's state. The values assigned to the properties determine the behaviour and appearance of that component. They are set through a setter method and can be obtained by a getter method.

Line 21 ⟶ 24:

:Persistence is the ability to save the current state of a Bean, including the values of a Bean's properties and instance variables, to nonvolatile storage and to retrieve them at a later time.

;Methods

:A beanBean should use [[Mutator_methodMutator method#Java_exampleJava example|accessor methods]] to [[Encapsulation_Encapsulation (computer_programmingcomputer programming)|encapsulate]] the properties. A beanBean can provide other methods for business logic not related to the access to the properties.

== Advantages ==

* The properties, events, and methods of a bean can be exposed to another application.

* A bean may register to receive events from other objects and can generate events that are sent to those other objects. {{citation needed|date=January 2023}}

* Auxiliary software can be provided to help configure a bean. {{citation needed|date=January 2023}}

*The configuration settings of a bean can be saved to persistent storage and restored. {{citation needed|date=January 2023}}

== Disadvantages ==

* A class with a [[nullary constructor|zero-argument constructor]] is subject to being instantiated in an invalid state.<ref name="Bloch">{{cite book|last1=Bloch|first1=Joshua|authorlink1=Joshua Bloch|title=Effective Java|date=2008|publisher=Addison-Wesley|isbn=978-0-321-35668-0|page=[https://archive.org/details/effectivejava00bloc_0/page/13 13]|edition=Second|url-access=registration|url=https://archive.org/details/effectivejava00bloc_0/page/13}}</ref> If such a class is instantiated manually by a developer (rather than automatically by some kind of framework), the developer might not realize that the class has been improperly instantiated. The compiler cannot detect such a problem, and even if it is documented, there is no guarantee that the developer will see the documentation.

* JavaBeans are inherently mutable and so lack the advantages offered by [[immutable objects]].<ref name="Bloch"/>

* Having to create getters for every property and setters for many, most, or all of them can lead to an immense quantity of [[boilerplate code]]. This can be mitigated using tools like [https://www.baeldung.com/intro-to-project-lombok Lombok].

== JavaBeans API ==

The JavaBeans functionality is provided by a set of classes and interfaces in the <ttcode>java.beans</ttcode> package.

{| class="wikitable sortable"

|-

Line 67 ⟶ 70:

* The class must have a public [[default constructor]] (with no arguments). This allows easy instantiation within editing and activation frameworks.

* The class [[property (programming)|properties]] must be accessible using ''get'', ''set'', ''is'' (can be used for boolean properties instead of get), ''to'' and other methods (so-called [[Accessor|accessor methods]] and [[mutator method]]s) according to a standard [[naming conventions (programming)|naming convention]]. This allows easy automated inspection and updating of bean state within frameworks, many of which include custom editors for various types of properties. Setters can have one or more than one argumentarguments.

* The class should be [[Serialization#Programming language support|serializable]]. (This allows applications and frameworks to reliably save, store, and restore the bean's state in a manner independent of the [[Virtual machine|VM]] and of the platform.)

Line 114 ⟶ 117:

/**

* Getter for property "deceased"

* Different syntax for a boolean field (is v.s.vs get)

*/

public boolean isDeceased() {

Line 178 ⟶ 181:

</html>

</syntaxhighlight>

== See also ==

* [[Software package (disambiguation)|Software packaging]]

==References==

Line 189 ⟶ 195:

[[Category:Java platform]]

[[Category:Articles with example Java code]]

[[Category:Architectural pattern (computer science)]]

[[Category:Software design patterns]]