java be an intro xi

8/6/2019 Java Be an Intro XI

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Java BeansJava Beans


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ContentContent

What is a Java Bean?What is a Java Bean?

BDKBDK What makes Bean possible?What makes Bean possible?

Support for Java BeanSupport for Java Bean

ReferencesReferences


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What are Java Beans?What are Java Beans?

Software ComponentSoftware Component

Specified interfaces.Specified interfaces.

Independent deployment.Independent deployment.

AnalogyAnalogy

Electronic components.Electronic components.

Automotive components.Automotive components.


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What are Java Beans? ...What are Java Beans? ...

Definition:Definition:

A Java bean is a reusable software component that canA Java bean is a reusable software component that canbe visuallymanipulated in builder tools.be visuallymanipulated in builder tools.

Java Bean TutorialsJava Bean Tutorials

TheThe JavaBeansJavaBeans SpecsSpecs areare availableavailable f orfordownloadingdownloading atat

httphttp:://java//java..sunsun..com/products/javabeans/docs/com/products/javabeans/docs/


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What is JavaBeans?What is JavaBeans? A Java Bean is a reusable softwareA Java Bean is a reusable software

component that can be manipulated visuallycomponent that can be manipulated visuallyin a builder toolin a builder tool JavaBeans is aJavaBeans is a portable, platformportable, platform--independent componentindependent component

modelmodel written in the Java programming language, developedwritten in the Java programming language, developedin collaboration with industry leaders.in collaboration with industry leaders.

It enables developers toIt enables developers towritewrite reusable componentsreusable components onceonceandand runrun themthem anywhereanywhere ---- benefiting from the platformbenefiting from the platform--independent powerof Java technology.independent powerof Java technology.

The goal of JavaBeans is to create a system wherebyThe goal of JavaBeans is to create a system wherebyapplication developers can take a setof beans from a stockapplication developers can take a setof beans from a stocklibrary and wire them together to make a full applicationlibrary and wire them together to make a full application


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Software ComponentsSoftware Components

A software component is a unit of

composition with contractually specified

interfaces and explicit context dependenciesonly. A software component can be deployed

independently and is subject to composition

by third parties.

Szyperski ECOOP96


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Composition not InheritanceComposition not InheritanceIn OO languages, new objects are created

from old using the inheritance mechanism.

Pluggable components are connected

together by composition rather than

inheritance.

Most of the flexibility of inheritance can

be gained from various compositionaltactics.


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Features of JavaBeansFeatures of JavaBeans

Support forSupport forintrospectionintrospection

so that a builder tool can analyze how a bean worksso that a builder tool can analyze how a bean works

Support forSupport forcustomizationcustomization

so that when using an application builder a user can customizeso that when using an application builder a user can customize

the appearance and behaviorof a beanthe appearance and behaviorof a bean Support forSupport foreventsevents

as a simple communication metaphor than can be used toas a simple communication metaphor than can be used toconnect up beansconnect up beans

Support forSupport forpropertiesproperties

both for customization and for programmatic useboth for customization and for programmatic use

Support forSupport forpersistencepersistence

so that a bean can be customized in an application builder andso that a bean can be customized in an application builder andthen have its customized state saved away and reloaded laterthen have its customized state saved away and reloaded later


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Persistent StoragePersistent Storage

Purpose:Purpose:

To use existing data formats and plug into OLE or OpenDocTo use existing data formats and plug into OLE or OpenDocdocuments (e.g., Excel doc inside a Word doc)documents (e.g., Excel doc inside a Word doc)

To be trivial for the common case of a tiny Bean (by saving itsTo be trivial for the common case of a tiny Bean (by saving itsinternal state)internal state)

SolutionsSolutions

ExternalizationExternalization: provides a Bean with full control over the: provides a Bean with full control over theresulting data layout.resulting data layout.

SerializationSerialization: provides an automatic wayof storingout and: provides an automatic wayof storingout andrestoring the internal state of a collection of Java objectsrestoring the internal state of a collection of Java objects

All bean must support either Serialization or ExternalizationAll bean must support either Serialization or Externalization


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What makes this possible?What makes this possible?

PropertiesProperties

EventsEvents

PersistencePersistence

IntrospectionIntrospection

CustomizationCustomization


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PropertiesProperties

Attributes.Attributes.

Can be read/write, readCan be read/write, read--onlyor writeonlyor write--only.only.

Several types of properties:Several types of properties:

SimpleSimple

IndexedIndexed

BoundBound

ConstrainedConstrained


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EventsEvents

Message sent from one object to another.Message sent from one object to another.

SenderSender firesfires event, recipient (listener)event, recipient (listener) handleshandlesthe eventthe event

There may be many listeners.There may be many listeners.

Event

source

Event

listenerFire event

Event

Object

Register listener


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Event

source

Event

Adapter

Fire eventEvent

Object

Register event listener

EventListener

Forward eventEvent

ObjectProvide

interface


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PersistencePersistence

Allows the graphical builder torecall theAllows the graphical builder torecall thestate of a bean.state of a bean.

public class Button implements java.io.Serializable { ... }public class Button implements java.io.Serializable { ... }

Selected property fields can bypass theSelected property fields can bypass the

serialization using keywordsserialization using keywords transienttransientororstaticstatic..


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IntrospectionIntrospection

A mechanism that allows the builder toolA mechanism that allows the builder toolto analyze a bean.to analyze a bean.

Two ways to analyze a bean:Two ways to analyze a bean:

lowlow--level reflection APIs.level reflection APIs.

vendor provided explicit informationvendor provided explicit information

(Customization).(Customization).

Application builder will provide defaultApplication builder will provide defaultBeanInfo classBeanInfo class BeanInfo.BeanInfo.


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ConclusionConclusion

Easy to use.Easy to use.

Difficult to build.Difficult to build.

Like all OO design, needs careful planning.Like all OO design, needs careful planning.

Similar to the String library in C++.Similar to the String library in C++.

Wide selection of JavaBeans in the future?Wide selection of JavaBeans in the future?


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SupportSupport

BDKBDK -- SunSun

NetBeansNetBeans www.netbeans.orgwww.netbeans.org

JbuilderJbuilder -- InpriseInprise

Super MojoSuper Mojo -- PenumbraSoftwarePenumbraSoftware

Visual Age for Java

Visual Age for Java -- IBMIBM

Visual CafeVisual Cafe -- Symantec CorporationSymantec Corporation

JDeveloper SuiteJDeveloper Suite -- OracleOracle


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ReferencesReferences

http://java.sun.com/products/javabeans/http://java.sun.com/products/javabeans/

Java Developer Connection TutorialsJava Developer Connection Tutorials

Java Beans, Part 1 to 4Java Beans, Part 1 to 4

http://developer.java.sun.com/developer/onlihttp://developer.java.sun.com/developer/onli

neTraining/neTraining/


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References...References...

Trail: JavaBeansTrail: JavaBeans

http://java.sun.com/docs/books/tutorial/javabhttp://java.sun.com/docs/books/tutorial/javab

eans/index.htmleans/index.html

JavaBeans 1.01 SpecificationJavaBeans 1.01 Specification

http://java.sun.com/beans/docs/spec.htmlhttp://java.sun.com/beans/docs/spec.html

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