JavaBeans

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JavaBeans
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What We Want

• Reusable components
• Components don't depend on other components
• Can configure a component visually and discover
  at "design time" the properites of the component
• Example clock
• we want a clock that can be easily added to any
  GUI application
• want to set things such as font, time, background
  color

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JavaBeans

• A JavaBean is
• a reusable component
• packaged as a JAR file containing one or more
  classes
• exposes properties and methods that other
  applications can use
• has a Facade Class (like a main class) with a
  default, no parameter constructor
• Facade class obeys the Java convention for
  get/set methods

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JavaBean Details

• A JavaBean must...
• implement java.io.Serializable
• contain a manifest that includes this value
• JavaBean true
• follow Java convention for naming get/set
  methods
• private String name
• public String getName() ...
• public void setName(String name) ...

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4 Kinds of Properties

• simple - property has a single value that is
  independent of changes to other properties
• indexed - (typically an array) a property that
  has many values, indexed by something
• bound - a property for which other Beans need to
  be notified whenever a change occurs
• constrained - the value of the property must be
  verified by another bean.

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Simple Property

• A title
• A boolean, read-only property

private String title public String getTitle( )
return title public String setTitle( String
title ) this.title title
private boolean full public boolean isFull( )
return full
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Indexed Property

• Indexed properties need 2 get and 2 set methods

/ course grades / private String grade /
get one grade / public String getGrade(int index
) return gradeindex / set one grade
/ public void setGrade( index index, String
value ) gradeindex value / get all
grades / public String getGrade( ) return
grades / set all grades / public void
setGrade(String newgrades) ...
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Bound Properties

• These are what make JavaBeans interesting
• Support "observers" using the PropertyChangeListen
  er interface

PropertyChangeListener propertyChange( e
PropertyChangeEvent )
PropertyChangeSupport - listeners Collection -
properties String many methods
addPropertyChangeListener(this)
YourJavaBean -setProperty( value )
firePropertyChange( "property", old, new )
AnObserverClass propertyChange( ... ) ...