Beans

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Beans
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Java Beans

• Reusable software component model 
• Class that follows a few coding standard
  (properties with getters/setters, includes
  default constructor)
• Class must be serializable (able to be stored in
  binary format)
• Facilitate rapid application development by
  assembling software components
• IDE is used to connect beans together... such as
  connecting animation bean to button bean
• JavaBeans are stored in Java Archive file (jar)
• Can be executed from jar, if includes main
• java -jar LogoAnimator.jar
• Commonly used with JSP and servlets

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Properties

• Instance variables can be used as JavaBean
  properties by defining set/get methods.
• For a variable propertyName, the methods should
  be
• public void setPropertyName(DataType value)
• public DataType getPropertyName()
• Note that the first letter is capitalized.
• Properties can be read-only (only a get method)
  or write-only (only a set method)

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Bound Properties

• A bound property causes the JavaBean that owns
  the property to notify other objects when the
  property's value changes. 
• Bean notifies its PropertyChangeListeners when
  the value changes.
• java.beans includes interface PropertyChangeListen
  er to facilitate
• Class PropertyChangeSupport provides listener
  registration and notification services.
• note property listeners/event handling not used
  with jsp

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SliderField Code

• public SliderFieldPanel()
• // create PropertyChangeSupport for bound
  properties
• changeSupport new PropertyChangeSupport(
  this )
• boxContainer.add( slider )
• slider.addChangeListener(
• new ChangeListener()
• // handle state change for JSlider
• public void stateChanged( ChangeEvent
  changeEvent )
• setCurrentValue( slider.getValue()
  )
• // end anonymous inner class

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SliderField Code

• SliderFieldPanel.java public void
  addPropertyChangeListener(
• PropertyChangeListener listener )
• changeSupport.addPropertyChangeListener(
  listener )

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SliderField Code

• public void setCurrentValue( int current )
• throws IllegalArgumentException
• if ( current lt 0 )
• throw new IllegalArgumentException()
• int oldValue currentValue
• // set currentValue property
• currentValue current
• // change slider and textfield values
• slider.setValue( currentValue )
• field.setText( String.valueOf( currentValue
  ) )
• // fire PropertyChange
• changeSupport.firePropertyChange(
  "currentValue",
• new Integer( oldValue ), new Integer(
  currentValue ) )

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Using the SliderField

• public class LogoAnimator3 extends LogoAnimator
• implements PropertyChangeListener
• public void
• propertyChange(PropertyChangeEvent e)
• setAnimationDelay(Integer.parseInt(
• e.getNewValue().toString()))

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Using the Slider Field

• // create new LogoAnimator2
• LogoAnimator3 animation new
  LogoAnimator3()
• // create new JFrame and add LogoAnimator3 to it
• JFrame application new JFrame( "Animator test"
  )
• application.getContentPane().add( animation,
• BorderLayout.CENTER )
• SliderFieldPanel slider new SliderFieldPanel()
• application.getContentPane().add(slider,
  BorderLayout.SOUTH)
• slider.addPropertyChangeListener(animation)

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Creating a JavaBean in Eclipse

• NOTE This does not seem to work with Eclipse
  3.2?
• Create your bean
• From the File Menu select the Export
• Select JAR file.  Press Next.
• Select the source file and your image directory. 
  Defaults should be "Export generated class files
  and resources" and "Compress files".  Enter a
  name for your jar file.  Press Next.
• I recommend that you don't export if you have
  compiler errors, but warnings are probably ok.
  Press Next.
• Generate the manifest and Seal the jar (for
  security, assures reader all files from same
  location).
• Select the class that contains main (e.g.,
  LogoAnimator.java).  Press Finish.
• You should have created a .jar file.
• Try to execute your file from the command line
  using the command java -jar yourfilename (e.g.,
  java -jar LogoAnimator.jar).  OR double-click
  from a Windows explorer.

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Creating a JavaBean jar from the command line

• Create your bean
• Create a manifest  which specifies the name and
  that it is a Java-Bean, and if it contains main
  (see example below)
• Name in manifest must use forward slashes (/),
  even if on Windows system
• Must specify Java-Bean True
• Note that Main-Class uses dots as separators
• Create the jar file jar cfm JarName.jar
  manifest.tmp package\.
• where c is for create, f says next argument is
  name of file, m indicates next parameter is the
  manifest name.
• The directory listed should include the class
  file(s) and any images needed.
• Example jar cfm LogoAnimator.jar manifest.tmp
  com\deitel\advjhtp1\beans\.
• If you have an images or other directory, it
  should be included in your directory structure
  above (i.e., an images directory under beans). 
  In the above example, you would have a class that
  would be in package com.deitel.advjhtp1.beans,
  which would have been compiled so that the class
  file is in the proper directory.
• Can verify with jar tvf JarName.jar
• where t is table of contents, v is verbose, f
  specifies next argument is name of jar file
• Try to execute your file from the command line
  using the command java -jar yourfilename (e.g.,
  java -jar LogoAnimator.jar). 

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Example manifest

• Main-Class com.deitel.advjhtp1.beans.LogoAnimator
  3
• Name com/deitel/advjhtp1/beans/LogoAnimator3.clas
  s
• Java-Bean True