Java Beans - Interview question & answers
What are Java Beans?
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.
What are externizable interface?
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.
What is bean persistance property?
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.What are the purpose of introspection?
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.
Why do I get a NullPointerException when loading a JAR file into the BeanBox?
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.
What is property editor in java beans?
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.Why are component architectures useful?
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.Why a component architecture for the Java platform?
JavaBeans brings the extraordinary power of the Java platform to component development, offering the ideal environment for a developer who wants to extend the concept of reusable component development beyond one platform and one architecture to embrace every platform and every architecture in the industry.What is the relationship between Sun s JFCs and JavaBeans?
The JFC (Java Foundation Classes) is based upon the AWT (Abstract Windowing Toolkit), which has been part of the Java platform from the beginning. JFC effectively adds a richer set of visual elements for building JavaBeans components and applications. See the JFC web site for more information.What are the security implications for downloading Beans over the Internet?
JavaBeans does not add any security features to the Java platform. Rather, JavaBeans components have full access to the broad range of security features that are part of the Java platform. JavaBeans components can be used to build a range of different kinds of solutions from full-fledged Java desktop applications to web-based Applets.
When will JavaBeans be supported on the [fill in the blank] platform/operating system?
The complete set of JavaBeans APIs are core to Java 2, hence any platform that is fully compatible with Java 2 implicitly supports JavaBeans. Thus, JavaBeans support will be available as soon as this platform/operating system vendor supports Java 2.Is the InfoBus client side only?
Yes. InfoBus is typically used to communicate among Beans at the client, and it can also be useful for sharing information among components at a single server site. The initial version of InfoBus is not distributed, and is therefore not intended for transmission of data between clients and servers. A variety of Java communication services, including JDBC, CORBA, and RMI can be used by InfoBus components for access to distributed data. For example, the ESuite Data Access component is a Bean that connects any JDBC compliant data source to the InfoBus. Once the data is on the bus, it can easily be imported by any InfoBus Data Consumer, such as a spreadsheet, chartingcomponent, word processor or data analysis tool.What is the relation between the InfoBus and RMI?
The InfoBus architecture addresses Beans talking to one in a single JVM not across multiple JVMs; while RMI (Remote Method Invocation) is intended for communication across JVMs (different Java Virtual Machines across the network). As for IIOP, one can envision a JavaBeans component that uses RMI to talk to something on another JVM and then publishes the data on the InfoBus. Additionally, RMI could be used to allow components in different security classes to communicate within the same JVM.Can JavaBeans use DCOM as its network model?
JavaBeans works with any network model (i.e., to communicate between components across the network), including CORBA, DCOM, etc. JavaBeans integrates well with CORBA IDL, which is an excellent solution for customers in a heterogeneous distributed computing environment with platform independent components. However, we recommend RMI for Java to Java inter-object communication.How and when will the JavaBeans Migration Assistant to ActiveX be available?
IBM plans to ship the JavaBeans Migration Assistant for ActiveX in Taligent's Visual Age, WebRunner Toolkit, and Visual Age for Java development tools. This will allow developers to utilize a common component model that may be leveraged by a wide range of tools, including the IBM Visual Age for Java family.
How to implement a bound property in your bean application?
► Import the java.beans package. This gives you access to the PropertyChangeSupport class.
► Instantiate a PropertyChangeSupport object. This object maintains the property change listener list and fires property change events. You can also make your class a PropertyChangeSupport subclass.
► Implement methods to maintain the property change listener list. Since a PropertyChangeSupport subclass implements these methods, you merely wrap calls to the property-change support object's methods.
► Modify a property's set method to fire a property change event when the property is changed.
Is JavaBeans a complete component architecture?
JavaBeans is a complete component model. It supports the standard component architecture features of properties, events, methods, and persistence. In addition, JavaBeans provides support for introspection (to allow automatic analysis of a JavaBeanscomponent) and customization (to make it easy to configure a JavaBeans component).
