CDW Most Frequently Asked Latest Advanced Java Interview Questions Answers
What Is Entity Reference?
A reference to an entity that is substituted for the reference when the XML document is parsed. It can reference a predefined entity such as or reference one that is defined in the DTD. In the XML data, the reference could be to an entity that is defined in the local subset of the DTD or to an external XML file (an external entity). The DTD can also carve out a segment of DTD specifications and give it a name so that it can be reused (included) at multiple points in the DTD by defining a parameter entity.
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.
Why Do I Get A Duplicate Name Error When Loading A Jar File?
The most common reason for a "java.lang.ClassFormatError: Duplicate name" error is that a .class file in the JAR contains a class whose class name is different from the expected name. So for example if you have a file called "a/B.class" and it contains a class called "B" or "a.X" instead of the class "a.B" then you will get this error.
The most common causes for this problem are either forgetting to include a "package a;" statement or having a "package" statement with the wrong name.
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.
Are There Javabeans Components Available That I Can Buy Today?
Yes. A large number of companies, both large and small, have announced their plans to deliver JavaBeans-based products.
What Kind Of Industry Support Exists For Javabeans?
A coalition of industry leaders in component development worked with JavaSoft to create the JavaBeans specification, which was released to the Internet for public comments on September 4, 1996. The "frozen" JavaBeans specification combines the work of Apple, Borland, IBM, JustSystem, Microsoft, Netscape, Rogue Wave, SunSoft and Symantec and many, many others... We're very pleased to see the tools community swiftly embracing JavaBeans by announcing support for JavaBeans in their visual application builder tools.
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.
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).
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.
What Is A Bean? Why Is Not A Bean An Applet?
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.
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
Write A Simple Bean Program?
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 );
}
}
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.
What Are The Purpose Of Introspection?
A growing number of Java object repository sites exist on the Internet in 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.
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.
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 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 The Different Kinds Of Enterprise Beans?
Stateless session bean- An instance of these non-persistent EJBs provides a service without storing an interaction or conversation state between methods. Any instance can be used for any client.
Stateful session bean-An instance of these non-persistent EJBs maintains state across methods and transactions. Each instance is associated with a particular client.
Entity bean-An instance of these persistent EJBs represents an object view of the data, usually rows in a database. They have a primary key as a unique identifier. Entity bean persistence can be either container-managed or bean-managed.
Message-drivenbean- An instance of these EJBs is integrated with the Java Message Service (JMS) to provide the ability for message-driven beans to act as a standard JMS message consumer and perform asynchronous processing between the server and the JMS message producer.
What Are The Methods Of Entity Bean?what Is The Difference Between Container-managed Persistent (cmp) Bean And Bean-managed Persistent(bmp) ?
Container-managed persistence beans are the simplest for the bean developer to create and the most difficult for the EJB server to support. This is because all the logic for synchronizing the bean's state with the database is handled automatically by the container. This means that the bean developer doesn't need to write any data access logic, while the EJB server is supposed to take care of all the persistence needs automatically. With CMP, the container manages the persistence of the entity bean. A CMP bean developer doesn't need to worry about JDBC code and transactions, because the Container performs database calls and transaction management instead of the programmer. Vendor tools are used to map the entity fields to the database and absolutely no database access code is written in the bean class. All table mapping is specified in the deployment descriptor. Otherwise, a BMP bean developer takes the load of linking an application and a database on his shoulders.
The bean-managed persistence (BMP) enterprise bean manages synchronizing its state with the database as directed by the container. The bean uses a database API to read and write its fields to the database, but the container tells it when to do each synchronization operation and manages the transactions for the bean automatically. Bean-managed persistence gives the bean developer the flexibility to perform persistence operations that are too complicated for the container or to use a data source that is not supported by the container.BMP beans are not 100% database-independent, because they may contain database-specific code, but CMP beans are unable to perform complicated DML (data manipulation language) statements. EJB 2.0 specification introduced some new ways of querying database (by using the EJB QL - query language).
What Is Software Architecture Of Ejb?
Session and Entity EJBs consist of 4 and 5 parts respetively
1. A remote interface (a client interacts with it),
2. A home interface (used for creating objects and for declaring business methods),
3. A bean object (an object, which actually performs business logic and EJB-specific operations).
4. A deployment descriptor (an XML file containing all information required for maintaining the EJB) or a set of deployment descriptors (if you are using some container-specific features).
5.A Primary Key class - is only Entity bean specific.
Can Entity Beans Have No Create() Methods?
Yes. In some cases the data is inserted NOT using Java application, so you may only need to retrieve the information, perform its processing, but not create your own information of this kind.
What Is Entity Reference?
A reference to an entity that is substituted for the reference when the XML document is parsed. It can reference a predefined entity such as or reference one that is defined in the DTD. In the XML data, the reference could be to an entity that is defined in the local subset of the DTD or to an external XML file (an external entity). The DTD can also carve out a segment of DTD specifications and give it a name so that it can be reused (included) at multiple points in the DTD by defining a parameter entity.
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.
Why Do I Get A Duplicate Name Error When Loading A Jar File?
The most common reason for a "java.lang.ClassFormatError: Duplicate name" error is that a .class file in the JAR contains a class whose class name is different from the expected name. So for example if you have a file called "a/B.class" and it contains a class called "B" or "a.X" instead of the class "a.B" then you will get this error.
The most common causes for this problem are either forgetting to include a "package a;" statement or having a "package" statement with the wrong name.
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.
Are There Javabeans Components Available That I Can Buy Today?
Yes. A large number of companies, both large and small, have announced their plans to deliver JavaBeans-based products.
What Kind Of Industry Support Exists For Javabeans?
A coalition of industry leaders in component development worked with JavaSoft to create the JavaBeans specification, which was released to the Internet for public comments on September 4, 1996. The "frozen" JavaBeans specification combines the work of Apple, Borland, IBM, JustSystem, Microsoft, Netscape, Rogue Wave, SunSoft and Symantec and many, many others... We're very pleased to see the tools community swiftly embracing JavaBeans by announcing support for JavaBeans in their visual application builder tools.
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| CDW Most Frequently Asked Latest Advanced Java Interview Questions Answers |
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.
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).
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.
What Is A Bean? Why Is Not A Bean An Applet?
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.
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
Write A Simple Bean Program?
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 );
}
}
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.
What Are The Purpose Of Introspection?
A growing number of Java object repository sites exist on the Internet in 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.
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.
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 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 The Different Kinds Of Enterprise Beans?
Stateless session bean- An instance of these non-persistent EJBs provides a service without storing an interaction or conversation state between methods. Any instance can be used for any client.
Stateful session bean-An instance of these non-persistent EJBs maintains state across methods and transactions. Each instance is associated with a particular client.
Entity bean-An instance of these persistent EJBs represents an object view of the data, usually rows in a database. They have a primary key as a unique identifier. Entity bean persistence can be either container-managed or bean-managed.
Message-drivenbean- An instance of these EJBs is integrated with the Java Message Service (JMS) to provide the ability for message-driven beans to act as a standard JMS message consumer and perform asynchronous processing between the server and the JMS message producer.
What Are The Methods Of Entity Bean?what Is The Difference Between Container-managed Persistent (cmp) Bean And Bean-managed Persistent(bmp) ?
Container-managed persistence beans are the simplest for the bean developer to create and the most difficult for the EJB server to support. This is because all the logic for synchronizing the bean's state with the database is handled automatically by the container. This means that the bean developer doesn't need to write any data access logic, while the EJB server is supposed to take care of all the persistence needs automatically. With CMP, the container manages the persistence of the entity bean. A CMP bean developer doesn't need to worry about JDBC code and transactions, because the Container performs database calls and transaction management instead of the programmer. Vendor tools are used to map the entity fields to the database and absolutely no database access code is written in the bean class. All table mapping is specified in the deployment descriptor. Otherwise, a BMP bean developer takes the load of linking an application and a database on his shoulders.
The bean-managed persistence (BMP) enterprise bean manages synchronizing its state with the database as directed by the container. The bean uses a database API to read and write its fields to the database, but the container tells it when to do each synchronization operation and manages the transactions for the bean automatically. Bean-managed persistence gives the bean developer the flexibility to perform persistence operations that are too complicated for the container or to use a data source that is not supported by the container.BMP beans are not 100% database-independent, because they may contain database-specific code, but CMP beans are unable to perform complicated DML (data manipulation language) statements. EJB 2.0 specification introduced some new ways of querying database (by using the EJB QL - query language).
What Is Software Architecture Of Ejb?
Session and Entity EJBs consist of 4 and 5 parts respetively
1. A remote interface (a client interacts with it),
2. A home interface (used for creating objects and for declaring business methods),
3. A bean object (an object, which actually performs business logic and EJB-specific operations).
4. A deployment descriptor (an XML file containing all information required for maintaining the EJB) or a set of deployment descriptors (if you are using some container-specific features).
5.A Primary Key class - is only Entity bean specific.
Can Entity Beans Have No Create() Methods?
Yes. In some cases the data is inserted NOT using Java application, so you may only need to retrieve the information, perform its processing, but not create your own information of this kind.
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