CG0165: Advanced Applications Development in Java

Michael BrockwaySajjad Shami

Week 5: JavaBeans

Northumbria University

School of Computing, Engineering & Information Sciences

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References

• Several slides in this lecture have made use of material with modifications provided by

• Mark Davidson: The Bean Builder Tutorial.• Deitel, Deitel & Santry: Advanced Java 2

Platform: How To Program 2002, Chapter 6 JavaBeans Component Model

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Outline

• Introduction

• Making a Bean class

• Jar files

• Bound Properties

• Custom events

• Bean Builder GUI and usage

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Introduction: JavaBeans (beans)

• Java’s reusable software component model

• rapid application development

• by assembling predefined software components i.e. reuse

• builder tools/IDEs: support beans

• applications/applets or even new beans!

• “component assembler” _ connecting the dots!

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• The JavaBeans Component model

– aims to make classes reusable components

– does this by means of standard structure and interface

– such a class may then be used by many common application builder tools

• it can be added to the "palette" of a tool bar

• it can be used as a component of a Java Server Page via the <jsp:useBean> tag

• etc

– a Bean class can be made to trigger or "fire" events

– examples: all the swing components JButton, JCheckbox, JScrollbar, JTextField, JTextArea, ... are JavaBeans

Introduction

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• In an IDE such as Sun's Forte or the more recent SunONE Studio or the free Bean Builder product from Sun,

– beans can be added to a palette along with other graphical components, controls, etc and

– their events are tied to event handlers by means of "wizards"

– the code is "generated".

Environment

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Example

• Consider a component assembler (CA) that has an animation bean

• bean has methods startAnimation() stopAnimation()

• Say, CA requires

• Beans can simply ‘connect’ the buttons to the methods!

• Builder tool does all the work (event-handling etc)

• Programmer: just needs to cover logistics!

Start Animation Stop Animation

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Benefits

• The ‘Animation bean’ and the ‘button beans’ do not need to know each other before assembly

• Button action is well known in Java

• CA uses the pre-existing button component to provide operation to the user

• Beans interact via defined services/methods

• www.java.sun.com/beans/

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• So what is it about a class that makes it a bean?

– The protected (or private) data, are a subset of them, make up the bean properties

– For each bean property Type prop there is a Type getProp() method and

– (Unless the property is read-only) a method void setProp(Type x)

– An indexed property is a data member which is an array of some data type.

– In this case there are two get methods

• A parameterless Type[] getProp () returns (a reference to) the array

• A method Type getProp(int i) returns the ith entry in the array

– A bean class implements Serializable• … so that it can be stored

• A simple example...

Making a Bean Class

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public class Student implements Serializable { protected String name; protected Date dob; protected boolean fullTime; protected int[] marks; //an indexed property public Student(String i, String n, Date d) { //constructor //.... } public String getName() { return name; } public void setName(String n) { name = n; } public Date getDob() { return dob; } public void setDob(Date d) { dob = d; }

public boolean isFullTime() { return fullTime; } public void setFullTime(boolean b) { fullTime = b; }

public int[] getMarks() { return marks; } public int getMarks(int i) { return marks[i]; } public void setMarks(int[] m) { marks = m; } public void setMarks(int i, int m) { marks[i] = m; }}

Example

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• the class LogoAnimator listed with these slides is another example: this time, a graphical JavaBean … a swing component

public class LogoAnimator extends JPanel ...

• class LogoAnimator implements the LogoAnimator JavaBean• LogoAnimator is a JavaBean containing an animated logo.• examine this class• LogoAnimator extends JPanel• implements interface serializable

• the class animationTimer (a Timer object) provides get and set methods for the animation time delay.

Another Example

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• JAR Stands for Java ARchive• A Jar is a kind of "zipped" set of Java classes and supporting files• To create LogoAnimator.jar

– jar cvf LogoAnimator.jar LogoAnimator.class• To create myJar.jar containing all classes & .dat files in current directory

– jar cvf myjar.jar *.class *.dat– The file specifications can also contain absolute or relative directory paths

• "v" is verbose option• To see contents of a jar

– jar tf myjar.jar• To extract a file or files from a jar

– jar xf myjar.jar file-spec• To update a jar

– jar uvf myjar.jar file-spec• To get a reminder of the main command-line options

– jar

• See ref http:java.sun.com/docs/books/tutorial/jar/index.html

Jars

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• A jar may contain a manifest in directory META-INF as file MANIFEST.MF

– You do not need one if you are simply archiving a whole lot of files in compressed format.

– You do need one if your jar is a complete Java application and you wish it to be “executable”, e.g. by double-clicking in windows

– You do need one if your jar houses a bean which you plan to deploy in an Integrated Development Tool

• You can create/edit the manifest: e.g. for LogoAnimator.jar,

– Save in manifest.tmp the text

Main-Class: LogoAnimator

Name: LogoAnimator.class

Java-Bean: True

Jars

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– ... then (if LogoAnimator.jar already exists) run• jar uvfm LogoAnimator.jar manifest.tmp

– Or if you are creating the jar,• jar cvfm LogoAnimator.jar manifest.tmp LogoAnimator.class• manifest.tmp has the text

• Jar creates MANIFEST.MF

– The optional Main-Class clause should refer to a class with a main method: it allows you to run the application by simply clicking the jar

– The Name: filename.class and Java-Bean: True lines (which must be preceded by a blank line) declare the jar to be a bean.

– These are used by "bean savvy" integrated development tools such as Forte or Sun Java Studio.

Jars

15 2002 Prentice Hall.All rights reserved.

Outline

Fig. 6.36 Method file manifest.tmpfor the Logo-Animator bean.

Line 1

Line 4

1 Main-Class: com.deitel.advjhtp1.beans.LogoAnimator2 3 Name: com/deitel/advjhtp1/beans/LogoAnimator.class4 Java-Bean: True

Class LogoAnimator contains method main, so virtual machines can execute the

application in this JAR file directly

Specify that LogoAnimatorshould be treated as a JavaBean

• To execute LogoAnimator from its JAR file• java –jar LogoAnimator.jar• Interpreter looks at the manifest file• Java Archive File (jars)

– contain JavaBeans– contains a manifest file

• describes JAR-file contents MANIFEST.MF

– placed in the META-INF directory in JAR file

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JavaBean Properties

• Property: Specific attribute of a JavaBean

– Read/Write property

• Defined as a set/get method pair of the form public void setPropertyName( DataType value ) public DataType getPropertyName()

• Builder tool inspects bean methods for these pairs– Process known as introspection

– Builder exposes that pair of methods as a property

• e.g., to expose the background property: public void setBackground( Color color ) public Color getBackground()

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Example

• Lets add animationDelay property to LogoAnimator

• We extend LogoAnimator to create LogoAnimator2 class

• New code has setAnimationDelay and getAnimationDelay

18 2002 Prentice Hall.All rights reserved.

Outline

Fig. 6.39 Logo-Animator2 with property animationDelay(part 1).

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Lines 16-25

1 // Fig. 6.39: LogoAnimator2.java2 // LogoAnimator2 extends LogoAnimator to include 3 // animationDelay property and implements ColorListener4 package com.deitel.advjhtp1.beans;5 6 // Java core packages7 import java.awt.*;8 import java.awt.event.*;9 10 // Java extension packages11 import javax.swing.*;12 13 public class LogoAnimator2 extends LogoAnimator {14 15 // set animationDelay property16 public void setAnimationDelay( int delay )17 {18 animationTimer.setDelay( delay );19 }20 21 // get animationDelay property22 public int getAnimationDelay()23 {24 return animationTimer.getDelay();25 }26 27 // launch LogoAnimator in JFrame for testing28 public static void main( String args[] )29 {30 // create new LogoAnimator231 LogoAnimator2 animation = new LogoAnimator2();32

Extend LogoAnimator to enable user to modify the rate of animation

Builder tool will expose animationDelay property

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Bound Properties

• Bound property– JavaBean notifies other objects when property

value changes• Accomplished via standard Java event-handling

features java.beans.PropertyChangeListener

» Listens for java.beans.PropertyChangeEvents

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• An important optional feature of a Java bean is the ability to fire events.

• Java core package java.beans includes

– class PropertyChangeEvent– interface PropertyChangeListener– class PropertyChangeSupport with methods

• firePropertyChange• addPropertyChangeListener• removePropertyChangeListener

• A bean equipped with a PropertyChangeSupport object can fire a PropertyChangeEvent by using the method firePropertyChange

– Registered listeners receive these events, in the form of PropertyChangeEvent objects

• A listener is any object implementing the PropertyChangeListener – It must implement void propertyChange(PropertyChangeEvent e)

Bound Properties

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• Example: the SliderFieldPanel

– A graphical “control” for input of numerical data

– Features a slider and a text box

• either can be used for input:

• on input, the other one updates its appearance

– The object as a whole fires a PropertyChangeEvent.

• LogoAnimatorTst1.java links this graphical bean to a LogoAnimator

Bound Properties

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Indexed Properties

• Indexed property

– Similar to standard property

– Array of primitives of objects public void setPropertyName( DataType[] data ) public void setPropertyName(int index, DataType data)

public DataType[] getPropertyName()public DataType getPropertyName( int index )

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• You can design your own events

– An event is an object of class extending class java.util.EventObject– It requires an interface extending interface java.util.EventListener

• A java bean can then work with events of this custom type

– Add/remove listeners

– Fire events

• Example: ColorSliderPanel.java bean

– Assembles THREE SliderFieldPanels into a JPanel– Uses these to set the red, green, blue components of the “colour property”

• indexed bean property int[] redGreenBlue

– Uses custom “ColorEvent” events, defined by class ColorEvent and interface ColorListener

– Maintains a set of listeners for these events

• Using java.util.HashSets– Fires a ColorEvent event when any of the three SliderFields is adjusted.

Custom Events

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• Example: ColorSliderPanel.java (ctd)

– Each SliderField component has a PropertyChangeListener which handles the PropertyChange by calling method setRedGreenBlue(...)

– setRedGreenBlue(...) updates the indexed bean property int[] redGreenBlue and then fires a ColorChanged event.

• LogoAnimatorTst2.java links this graphical bean to a LogoAnimator

• adjusts the logo animator’s background colour in response to the ColorSliderPanel

Custom Events

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The Bean Builder GUI

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The Bean Builder GUI

The Design Panel

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The Demo Application

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The Palette

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Instantiating the First Component: The JScrollPane

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Instantiating Other Components

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The Property Inspector

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Editing Properties of Objects

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Creating a Non-visual Bean

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Setting an Object as a Property of Another

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Creating Event Adapters

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Testing the Runtime Application

• The live object graph can be tested by taking it out of Design Mode and putting it into Runtime Mode

• The two states are switchable

• In the Runtime Mode

• the objects become live

• The application behaves exactly as the way it was designed

• Type some entries in the text field:

• Press ‘Remove All

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Using SpringLayout

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• WWW Resources

– Look at the links from http://java.sun.com/products/javabeans/

– http://java.sun.com/products/javabeans/beanbuilder/index.html

• The Bean Builder is (besides Forte for Java and Sun Java Studio) another bean-based visual application developer.

– http://java.sun.com/products/javabeans/docs/spec.html

– The API reference http://java.sun.com/j2se/1.4.1/docs/api/

• Look up package java.beans

• The Deitel et al textbook references cited above.

Further Reading