This document discusses JavaBeans, which are reusable Java components that can be visually manipulated in application builder tools. JavaBeans follow certain conventions like having a no-argument constructor and getter/setter methods for properties. They can represent user interface elements like buttons and text boxes, and be assembled visually into applications. The document covers the components of JavaBeans, how they are assembled, advantages of using JavaBeans, and the steps to create a JavaBean class.

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Java Beans

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Components
• Hardware components of Integrated
Circuits – Resistors, Capacitors and
Inductors
• All of these components can be reused in
different type of circuits
• Software components – buttons,
textboxes, checkboxes, radio buttons
• The above mentioned components can be
used in the following applications:
– Calculator
– Railway reservation system
– Online polling system etc.,

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Components Assembly
• Assembly is one of the key features of Java Bean
though no not specific solution is provided.
– Different ways of assembling components are
supplied.
Component-based assembly Heterogeneous assembly

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What are beans?
• Reusable Java code
• Easiest to reuse is static objects;
– Ex: Text fields, buttons
– Available as third-party products
– Limited interaction with environment
– The functionality does not change
• Can be composed into complex beans
• Drag-and-drop using application
construction tools

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What is a Java Bean?
• A component technology for Java that
allows a developer to create reusable
software objects.
• A Java Bean is a reusable software
component that can be visually
manipulated in builder tools( during the
software development).
• A Java Bean is a software component that
has been designed to be reusable in a
variety of different environments.

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Advantages of Java Beans
• Obtains all the benefits of Java (write-once, run-anywhere)
• The properties, events and methods of a bean
that are exposed to an application builder tool can
be controlled
• A Bean may be designed to operate correctly in
different locales
• Auxiliary software can be provided to help a
person configure a Bean
• The configuration settings of a Bean can be saved
in persistent storage and restored at a later time
• A Bean may register to receive events from other
objects and can generate events that are sent to
other objects

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Application Builder Tools
• A utility that enables the user to configure
a set of Beans, connect them together,
and produce a working application
– A palette is provided that lists all of the
available Beans
– A worksheet is displayed that allows the
designer to lay out Beans in a GUI. A designer
may drag and drop a Bean from the palette to
this worksheet
– Special editors and customizers allow a Bean
to be configured
– Commands allow a designer to inquire about
the state and behavior of a Bean
– Capabilities exist to interconnect beans

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Design Patterns for Properties
A property is a subset of a Bean’s state
• Simple properties
• Boolean properties
• Indexed properties

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Simple and Boolean properties
// member used to store property value //
private String internalString;
// set and get method for property named String //
public void setString(String newValue)
{ internalString = newValue; }
public String getString()
{ return internalString; }
// member used to store property value //
private boolean connect;
// set and get method for boolean property name connected //
public void setConnected(boolean newValue)
{ connect = newValue; }
public boolean isConnected(} { return connect; }

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Indexed properties
• An indexed property represent a
array of values. And we can use
additional get and set methods for an
indexed property. This get and set
method take an integer index
parameter. This index parameter
indicates the place in the array where
the new property value has to be put.

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Indexed properties
// member to store indexed property //
private int[] numbers = {1, 2, 3, 4};
// set and get method for complete array //
public void setNumbers(int[] newValue)
{
numbers = newValue;
}
public int[] getNumbers()
{
return numbers;
}

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Indexed properties
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// set and get method with index to set one element
of array //
public void setNumbers(int index, int newValue)
{
numbers[index] = newValue;
}
public int getNumbers(int index)
{
return numbers[index];
}

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Bean Class
A bean is a Java class that:
– Has a void constructor
– Has private instance variables with setter and getter
– Methods
public class SimpleBean
{
private int counter;
SimpleBean() {counter=0;}
int getCounter() {return counter;}
void setCounter(int c) {counter=c;}
}

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Steps involved in Creating a Java Bean
a. Write the SimpleBean code.
b. Create a manifest, the JAR file, and the class
file SimpleBean.class.
c. Load the JAR file (using NetBeans)
– Start NetBeans.
– From the File menu select "New Project" to create a new
application for your bean. You can use "Open Project" to
add your bean to an existing application.
– Create a new application using the New Project Wizard.
– Select a newly created project in the List of Projects,
expand the Source Packages node, and select the
Default Package element.
– Click the right mouse button and select New|JFrameForm
from the pop-up menu.
– Select the newly created Form node in the Project Tree.
A blank form opens in the GUI Builder view of an Editor
tab.

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Steps involved in Creating a Java Bean
continued
– Open the Palette Manager for Swing/AWT
components by selecting Palette Manager in the Tools
menu.
– In the Palette Manager window select the beans
components in the Palette tree and press the "Add
from JAR" button.
– Specify a location for your SimpleBean JAR file and
follow the Add from JAR Wizard instructions.
– Select the Palette and Properties options from the
Windows menu.
– Expand the beans group in the Palette window. The
SimpleBean object appears. Drag the SimpleBean
object to the GUI Builder panel.
d. Inspect Properties and Events

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JAR Files
– A JAR file allows to efficiently deploy a
set of classes and their associated
resources
– Elements in a JAR file are compressed
– Digital signatures may also be
associated with the individual elements
in a JAR file

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Manifest Files
– To indicate which of the components in a JAR
file are Java Beans
– Example
• d:/demo/one.gif
• d:/demo/two.gif
• d:/demo/three.gif
• d:/demo/one.class
Java- Bean:True
– A manifest file may reference several .class
files. If a .class file is a Java Bean, its entry
must be immediately followed by the line
“Java- Bean:True”.

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Deployed Bean
import java.awt.Color;
import javax.swing.JLabel;
import java.io.Serializable;
public class SimpleBean extends JLabel
implements Serializable {
public SimpleBean() {
setText( "Hello world!" );
setOpaque( true );
setBackground( Color.BLUE );
setForeground( Color.YELLOW );
}
}