Java Beans Interview Preparation Guide

Java Beans are usual Java classes which adhere to certain coding conventions:
► Implements java.io.Serializable interface
► Provides no argument constructor
► Provides getter and setter methods for accessing it's properties.

Usually this is because of a mistake in the JAR file being loaded. In the meantime, typical errors include:

► The MANIFEST file uses classes using the wrong file separator ("/" should be used in all platforms).
► The MANIFEST file refers to classes in a package but the actual .class files are not really in that package.

A bean has the property of persistence when its properties, fields, and state information are saved to and retrieved from storage. Component models provide a mechanism for persistence that enables the state of components to be stored in a non-volatile place for later retrieval.

Use the Externalizable interface when you need complete control over your bean's serialization (for example, when writing and reading a specific file format).
To use the Externalizable interface you need to implement two methods: readExternal and writeExternal. Classes that implement Externalizable must have a no-argument constructor.

A growing number of Java object repository sites exist on the Internet in answer to the demand for centralized deployment of applets, classes, and source code in general. Any developer who has spent time hunting through these sites for licensable Java code to incorporate into a program has undoubtedly struggled with issues of how to quickly and cleanly integrate code from one particular source into an application.

The way in which introspection is implemented provides great advantages, including:

► Portability - Everything is done in the Java platform, so you can write components once, reuse them everywhere. There are no extra specification files that need to be maintained independently from your component code. There are no platform-specific issues to contend with. Your component is not tied to one component model or one proprietary platform. You get all the advantages of the evolving Java APIs, while maintaining the portability of your components.
► Reuse - By following the JavaBeans design conventions, implementing the appropriate interfaces, and extending the appropriate classes, you provide yourcomponent with reuse potential that possibly exceeds your expectations.

A property editor is a tool for customizing a particular property type. Property editors are activated in the Properties window. This window determines a property's type, searches for a relevant property editor, and displays the property's current value in a relevant way.

Write the SimpleBean code. Put it in a file named SimpleBean.java, in the directory of your choice. Here's the code:

import java.awt.Color;
import java.beans.XMLDecoder;
import javax.swing.JLabel;
import java.io.Serializable;

public class SimpleBean extends JLabel
implements Serializable {
public SimpleBean() {
setText( "Hello world!" );
setOpaque( true );
setBackground( Color.RED );
setForeground( Color.YELLOW );
setVerticalAlignment( CENTER );
setHorizontalAlignment( CENTER );
}
}

A Java Bean is a software component written in the Java programming language that conforms to the JavaBeans component specification. The JavaBeans APIs became part of the "core" Java APIs as of the 1.1 release of the JDK.
The JavaBeans specification defines a Java-based software component model that adds a number of features to the Java programming language. Some of these features include:

► introspection
► customization
► events
► properties
► persistence

Enterprise JavaBeans (EJBs) are Java-based software components that are built to comply with Java's EJB specification and run inside of an EJB container supplied by a J2EE provider. An EJB container provides distributed application functionality such as transaction support, persistence and lifecycle management for the EJBs.

JavaBeans components, or Beans, are reusable software components that can be manipulated visually in a builder tool. Beans can be combined to create traditional applications, or their smaller web-oriented brethren, applets. In addition, applets can be designed to work as reusable Beans.

Individual Beans will function quite differently, but typical unifying features that distinguish a Bean are:

► Introspection: enables a builder tool to analyze how a Bean works
► Customization: enables a developer to use an app builder tool to customize the appearance and behavior of a Bean
► Events: enables Beans to communicate and connect together
► Properties: enable developers to customize and program with Beans
► Persistence: enables developers to customize Beans in an app builder, and then retrieve those Beans, with customized features intact, for future use.

Developers are turning to creating components rather than monolithic applications to free themselves from slow, expensive application development, and to build up a portable, reusable code base. This enables developers to quickly attack new market opportunities, new joint development opportunities, and new ways to sell smaller packages of software.