2. Introduction
Every Java user interface class is a JavaBeans component.
Java Beans makes it easy to reuse software components.
Developers can use software components written by others
without having to understand their inner workings.
Ravi Kant Sahu, Asst. Professor @ Lovely Professional University, Punjab (India)
3. Java Beans
JavaBeans is a software component architecture that extends the
power of the Java language by enabling well-formed objects to
be manipulated visually at design time in a pure Java builder
tool.
It is a reusable software component.
A JavaBean is a specially constructed Java class written in the
Java and coded according to the JavaBeans API specifications.
Ravi Kant Sahu, Asst. Professor @ Lovely Professional University, Punjab (India)
4. Java Beans Specifications
1.
2.
3.
4.
5.
A bean must be a public class.
A bean must have a public no-arg constructor, though it can have
other constructors if needed.
public MyBean();
A bean must implement the Serializable interface to ensure a
persistent state.
It should provide methods to set and get the values of the
properties, known as getter (accessor) and setter (mutator)
methods.
A bean may have events with correctly constructed public
registration and deregistration methods that enable it to add and
remove listeners.
Ravi Kant Sahu, Asst. Professor @ Lovely Professional University, Punjab (India)
5. Java Beans Specification
The first three requirements must be observed, and therefore
are referred to as minimum JavaBeans component
requirements.
The last two requirements depend on implementations.
It is possible to write a bean component without get/set
methods and event registration/deregistration methods.
Ravi Kant Sahu, Asst. Professor @ Lovely Professional University, Punjab (India)
6. Java Beans Example
public class StudentsBean implements java.io.Serializable
{ private String firstName = null;
private String lastName = null;
private int age = 0;
public StudentsBean() { }
public String getFirstName() { return firstName; }
public String getLastName(){ return lastName; }
public int getAge(){ return age; }
public void setFirstName(String firstName)
{ this.firstName = firstName; }
public void setLastName(String lastName)
{ this.lastName = lastName; }
public void setAge(Integer age){ this.age = age; } }
Ravi Kant Sahu, Asst. Professor @ Lovely Professional University, Punjab (India)
7. Java Beans Component
The classes that define the beans, referred to as JavaBeans
components or bean components.
A JavaBeans component is a serializable public class with a
public no-arg constructor.
Ravi Kant Sahu, Asst. Professor @ Lovely Professional University, Punjab (India)
8. Bean Properties
Properties are discrete, named attributes of a Java bean that can
affect its appearance or behavior.
They are often data fields of a bean.
For example, JButton component has a property named text.
Accessor and mutator methods are provided to let the user read
and write the properties.
Ravi Kant Sahu, Asst. Professor @ Lovely Professional University, Punjab (India)
9. Property-Naming Patterns
The bean property-naming pattern is a convention of the
JavaBeans component model that simplifies the bean developer's
task of presenting properties.
A property can be a primitive data type or an object type.
The property type dictates the signature of the accessor and
mutator methods.
Note: Properties describe the state of the bean. Naturally, data
fields are used to store properties.
Ravi Kant Sahu, Asst. Professor @ Lovely Professional University, Punjab (India)
10. Accessor Methods
The accessor method is named get<PropertyName>(), which
takes no parameters and returns a primitive type value or an
object of a type identical to the property type.
public String getMessage()
public int getXCoordinate()
public int getYCoordinate()
Ravi Kant Sahu, Asst. Professor @ Lovely Professional University, Punjab (India)
11.
For a property of boolean type, the accessor method should be
named
is<PropertyName>( )
which returns a boolean value.
For example:
public boolean isCentered()
Ravi Kant Sahu, Asst. Professor @ Lovely Professional University, Punjab (India)
12. Mutator Methods
The mutator method should be named as
set<PropertyName>(dataType p)
which takes a single parameter identical to the property type and
returns void.
public void setMessage(String s)
public void setXCoordinate(int x)
public void setYCoordinate(int y)
public void setCentered(boolean centered)
Ravi Kant Sahu, Asst. Professor @ Lovely Professional University, Punjab (India)
13. Java EvEnt ModEl
Ravi Kant Sahu, Asst. Professor @ Lovely Professional University, Punjab (India)
14. Event Delegation Model
The Java event delegation model provides the foundation for
beans to send, receive, and handle events.
The Java event model consists of the following three types of
elements:
The event object: An event object contains the information that
describes the event.
The source object: A source object is where the event originates.
When an event occurs on a source object, an event object is created.
The event listener object: An object interested in the event handles
the event. Such an object is called a listener.
Ravi Kant Sahu, Asst. Professor @ Lovely Professional University, Punjab (India)
15. Event classes and Event Listener interfaces
An event object is created using an event class, such as
ActionEvent, MouseEvent, and ItemEvent.
Ravi Kant Sahu, Asst. Professor @ Lovely Professional University, Punjab (India)
16. Source Components
The source component contains the code that detects an
external or internal action that triggers the event.
Upon detecting the action, the source should fire an event
to the listeners by invoking the event handler defined by
the listeners.
The source component must also contain methods for
registering and deregistering listeners.
Ravi Kant Sahu, Asst. Professor @ Lovely Professional University, Punjab (India)
17. Ravi Kant Sahu, Asst. Professor @ Lovely Professional University, Punjab (India)
18. Listener Components
A listener component for an event must implement the event
listener interface.
The object of the listener component cannot receive event
notifications from a source component unless the object is
registered as a listener of the source.
A listener component may implement any number of listener
interfaces to listen to several types of events.
A source component may register many listeners. A source
component may register itself as a listener.
Ravi Kant Sahu, Asst. Professor @ Lovely Professional University, Punjab (India)
19. Ravi Kant Sahu, Asst. Professor @ Lovely Professional University, Punjab (India)
20. Creating Custom Source Components
A source component must have the appropriate
registration and deregistration methods for adding and
removing listeners.
Events can be unicasted (only one listener object is
notified of the event) or multicasted (each object in a
list of listeners is notified of the event).
Ravi Kant Sahu, Asst. Professor @ Lovely Professional University, Punjab (India)
21. Unicast
public void add<Event>Listener(<Event>Listener l)
throws TooManyListenersException;
Multicast
The naming pattern for adding a multicast listener is the same,
except that it does not throw the TooManyListenersException.
public void add<Event>Listener(<Event>Listener l)
Ravi Kant Sahu, Asst. Professor @ Lovely Professional University, Punjab (India)
22. Deregistration Method
The naming pattern for removing a listener (either
unicast or multicast)
public void remove<Event>Listener(<Event>Listener l)
Ravi Kant Sahu, Asst. Professor @ Lovely Professional University, Punjab (India)
23. Creating Java Beans
Step 1: Create a Java Bean file e.g. “LightBulb.java”
Step 2: Compile the file: javac LightBulb.java
Step 3: Create a manifest file, named “manifest.tmp”
Step 4: Create the JAR file, named “LightBulb.jar”
Step 5: Load jar file.
Ravi Kant Sahu, Asst. Professor @ Lovely Professional University, Punjab (India)
24. Manifest File
Create text file manifest.tmp
Manifest file describes contents of JAR file
Name: name of file with bean class
Java-Bean: true - file is a JavaBean
Ravi Kant Sahu, Asst. Professor @ Lovely Professional University, Punjab (India)
25. Creating Jar file
c - creating JAR file
f - indicates next argument is name of file
m - next argument manifest.tmp file
Used to create MANIFEST.MF
Ravi Kant Sahu, Asst. Professor @ Lovely Professional University, Punjab (India)
26. Ravi Kant Sahu, Asst. Professor @ Lovely Professional University, Punjab (India)
