Advanced Java FAQ

Advanced Java FAQ - 17

1.What is "application client" ?

A first-tier J2EE client component that executes in its own Java virtual machine. Application clients have access to some J2EE platform APIs.

2.What is "application client container" ?

A container that supports application client components.

3.What is "application client module" ?

A software unit that consists of one or more classes and an application client deployment descriptor.

4.What are the four types of J2EE modules?

1. Application client module
2. Web module
3. Enterprise JavaBeans module
4. Resource adapter module

5.What does application client module contain?

The application client module contains:
--class files,
--an application client deployment descriptor.
Application client modules are packaged as JAR files with a .jar extension.

6.What does web module contain?

The web module contains:
--JSP files,
--class files for servlets,
--GIF and HTML files, and
--a Web deployment descriptor.
Web modules are packaged as JAR files with a .war (Web ARchive) extension.

7.What are the differences between Ear, Jar and War files? Under what circumstances should we use each one?

There are no structural differences between the files; they are all archived using zip-jar compression. However, they are intended for different purposes.
--Jar files (files with a .jar extension) are intended to hold generic libraries of Java classes, resources, auxiliary files, etc.
--War files (files with a .war extension) are intended to contain complete Web applications. In this context, a Web application is defined as a single group of files, classes, resources, .jar files that can be packaged and accessed as one servlet context.
--Ear files (files with a .ear extension) are intended to contain complete enterprise applications. In this context, an enterprise application is defined as a collection of .jar files, resources, classes, and multiple Web applications.
Each type of file (.jar, .war, .ear) is processed uniquely by application servers, servlet containers, EJB containers, etc.

8.What is the difference between Session bean and Entity bean ?

The Session bean and Entity bean are two main parts of EJB container.
Session Bean
--represents a workflow on behalf of a client
--one-to-one logical mapping to a client.
--created and destroyed by a client
--not permanent objects
--lives its EJB container(generally) does not survive system shut down
--two types: stateless and stateful beans
Entity Bean
--represents persistent data and behavior of this data
--can be shared among multiple clients
--persists across multiple invocations
--findable permanent objects
--outlives its EJB container, survives system shutdown
--two types: container managed persistence(CMP) and bean managed persistence(BMP)

9.What is "applet"  ?

A J2EE component that typically executes in a Web browser but can execute in a variety of other applications or devices that support the applet programming model.

10.What are the components of J2EE application?

A J2EE component is a self-contained functional software unit that is assembled into a J2EE application with its related classes and files and communicates with other components. The J2EE specification defines the following J2EE components:
   Application clients and applets are client components.
   Java Servlet and JavaServer PagesTM (JSPTM) technology components are web components.
   Enterprise JavaBeansTM (EJBTM) components (enterprise beans) are business components.
   Resource adapter components provided by EIS and tool vendors.

11.What is "applet container"  ?

A container that includes support for the applet programming model.

12.What is "application assembler" ?

A person who combines J2EE components and modules into deployable application units.

13.What is authentication ?

The process that verifies the identity of a user, device, or other entity in a computer system, usually as a prerequisite to allowing access to resources in a system. The Java servlet specification requires three types of authentication-basic, form-based, and mutual-and supports digest authentication.

14.What is authorization ?

The process by which access to a method or resource is determined. Authorization depends on the determination of whether the principal associated with a request through authentication is in a given security role. A security role is a logical grouping of users defined by the person who assembles the application. A deployer maps security roles to security identities. Security identities may be principals or groups in the operational environment.

15.What is "application component provider" ?

A vendor that provides the Java classes that implement components' methods, JSP page definitions, and any required deployment descriptors.

16.What is "application configuration resource file" ?

An XML file used to configure resources for a Java Server Faces application, to define navigation rules for the application, and to register converters, Validator, listeners, renders, and components with the application.

17.What is J2EE?

J2EE is an environment for developing and deploying enterprise applications. The J2EE platform consists of a set of services, application programming interfaces (APIs), and protocols that provide the functionality for developing multitier, web-based applications.

18.What is the J2EE module?

A J2EE module consists of one or more J2EE components for the same container type and one component deployment descriptor of that type.

19.What is "archiving" ?

The process of saving the state of an object and restoring it.

20.What is "asant" ?

A Java-based build tool that can be extended using Java classes. The configuration files are XML-based, calling out a target tree where various tasks get executed.

21.What is "attribute"?

A qualifier on an XML tag that provides additional information.

22.What is authorization constraint ?

An authorization rule that determines who is permitted to access a Web resource collection.

23.What is B2B ?

B2B stands for Business-to-business.

24.What is caller principal ?

The principal that identifies the invoker of the enterprise bean method.

25.What is cascade delete ?

A deletion that triggers another deletion. A cascade delete can be specified for an entity bean that has container-managed persistence.

26.What is bean-managed persistence ?

The mechanism whereby data transfer between an entity bean's variables and a resource manager is managed by the entity bean.

27.What is bean-managed transaction ?

A transaction whose boundaries are defined by an enterprise bean.

28.What is binding (XML) ?

Generating the code needed to process a well-defined portion of XML data.

29.What is backing bean ?

A JavaBeans component that corresponds to a JSP page that includes JavaServer Faces components. The backing bean defines properties for the components on the page and methods that perform processing for the component. This processing includes event handling, validation, and processing associated with navigation.

30.What is basic authentication ?

An authentication mechanism in which a Web server authenticates an entity via a user name and password obtained using the Web application's built-in authentication mechanism.

31.What is callback methods ?

Component methods called by the container to notify the component of important events in its life cycle.

32.What is caller ?

Same as caller principal.

33.What is business logic ?

The code that implements the functionality of an application. In the Enterprise JavaBeans architecture, this logic is implemented by the methods of an enterprise bean.

34.What is business method ?

A method of an enterprise bean that implements the business logic or rules of an application.

35.What is binding (JavaServer Faces technology) ?

Wiring UI components to back-end data sources such as backing bean properties.

36.What is container-managed persistence ?

The mechanism whereby data transfer between an entity bean's variables and a resource manager is managed by the entity bean's container.

37.What is container-managed sign-on ?

The mechanism whereby security information needed for signing on to a resource is supplied by the container.

38.What is CORBA ?

Common Object Request Broker Architecture. A language-independent distributed object model specified by the OMG.

39.What is create method ?

A method defined in the Interview Questions - Home interface and invoked by a client to create an enterprise bean.

40.What is credentials ?

The information describing the security attributes of a principal.

41.What is container-managed transaction ?

A transaction whose boundaries are defined by an EJB container. An entity bean must use container-managed transactions.

42.What is conversational state ?

The field values of a session bean plus the transitive closure of the objects reachable from the bean's fields. The transitive closure of a bean is defined in terms of the serialization protocol for the Java programming language, that is, the fields that would be stored by serializing the bean instance.

43.What is CSS ?

Cascading style sheet. A stylesheet used with HTML and XML documents to add a style to all elements marked with a particular tag, for the direction of browsers or other presentation mechanisms.

44.What is CTS ?

Compatibility test suite. A suite of compatibility tests for verifying that a J2EE product complies with the J2EE platform specification.

45.What is data ?

The contents of an element in an XML stream, generally used when the element does not contain any subelements. When it does, the term content is generally used. When the only text in an XML structure is contained in simple elements and when elements that have subelements have little or no data mixed in, then that structure is often thought of as XML data, as opposed to an XML document.

46.What is DDP ?

Document-driven programming. The use of XML to define applications.

47.What is content ?

In an XML document, the part that occurs after the prolog, including the root element and everything it contains.

48.What is context attribute ?

An object bound into the context associated with a servlet.

49.What is context root ?

A name that gets mapped to the document root of a Web application.

50.What is declaration ?

The very first thing in an XML document, which declares it as XML. The minimal declaration is . The declaration is part of the document prolog.

51.What is declarative security ?

Mechanisms used in an application that are expressed in a declarative syntax in a deployment descriptor.

52.What is delegation ?

An act whereby one principal authorizes another principal to use its identity or privileges with some restrictions.

53.What is deployer ?

A person who installs J2EE modules and applications into an operational environment.

54.What is build file ?

The XML file that contains one or more asant targets. A target is a set of tasks you want to be executed. When starting asant, you can select which targets you want to have executed. When no target is given, the project's default target is executed.

55.What is CDATA ?

A predefined XML tag for character data that means "don't interpret these characters," as opposed to parsed character data (PCDATA), in which the normal rules of XML syntax apply. CDATA sections are typically used to show examples of XML syntax.

56.What is certificate authority ?

A trusted organization that issues public key certificates and provides identification to the bearer.

57.What is client-certificate authentication ?

An authentication mechanism that uses HTTP over SSL, in which the server and, optionally, the client authenticate each other with a public key certificate that conforms to a standard that is defined by X.509 Public Key Infrastructure.

58.What is comment ?

In an XML document, text that is ignored unless the parser is specifically told to recognize it.

59.What is component-managed sign-on ?

A mechanism whereby security information needed for signing on to a resource is provided by an application component.

60.What is connector ?

A standard extension mechanism for containers that provides connectivity to enterprise information systems. A connector is specific to an enterprise information system and consists of a resource adapter and application development tools for enterprise information system connectivity. The resource adapter is plugged in to a container through its support for system-level contracts defined in the Connector architecture.

61.What is commit ?

The point in a transaction when all updates to any resources involved in the transaction are made permanent.

62.What is component contract ?

The contract between a J2EE component and its container. The contract includes life-cycle management of the component, a context interface that the instance uses to obtain various information and services from its container, and a list of services that every container must provide for its components.

63.What is deployment ?

The process whereby software is installed into an operational environment.

64.What is deployment descriptor ?

An XML file provided with each module and J2EE application that describes how they should be deployed. The deployment descriptor directs a deployment tool to deploy a module or application with specific container options and describes specific configuration requirements that a deployer must resolve.

65.What is document ?

In general, an XML structure in which one or more elements contains text intermixed with subelements.

66.What is Document Object Model ?

An API for accessing and manipulating XML documents as tree structures. DOM provides platform-neutral, language-neutral interfaces that enables programs and scripts to dynamically access and modify content and structure in XML documents.

67.What is document root ?

The top-level directory of a WAR. The document root is where JSP pages, client-side classes and archives, and static Web resources are stored.

68.What is DTD ?

Document type definition. An optional part of the XML document prolog, as specified by the XML standard. The DTD specifies constraints on the valid tags and tag sequences that can be in the document. The DTD has a number of shortcomings, however, and this has led to various schema proposals. For example, the DTD entry says that the XML element called username contains parsed character data-that is, text alone, with no other structural elements under it. The DTD includes both the local subset, defined in the current file, and the external subset, which consists of the definitions contained in external DTD files that are referenced in the local subset using a parameter entity.

69.What is destination ?

A JMS administered object that encapsulates the identity of a JMS queue or topic. See point-to-point messaging system, publish/subscribe messaging system.

70.What is digest authentication ?

An authentication mechanism in which a Web application authenticates itself to a Web server by sending the server a message digest along with its HTTP request message. The digest is computed by employing a one-way hash algorithm to a concatenation of the HTTP request message and the client's password. The digest is typically much smaller than the HTTP request and doesn't contain the password.

71.What is distributed application ?

An application made up of distinct components running in separate runtime environments, usually on different platforms connected via a network. Typical distributed applications are two-tier (client-server), three-tier (client-middleware-server), and multitier (client-multiple middleware-multiple servers).

72.What is durable subscription ?

In a JMS publish/subscribe messaging system, a subscription that continues to exist whether or not there is a current active subscriber object. If there is no active subscriber, the JMS provider retains the subscription's messages until they are received by the subscription or until they expire.

73.What is JavaServer Faces expression language ?

A simple expression language used by a JavaServer Faces UI component tag attributes to bind the associated component to a bean property or to bind the associated component's value to a method or an external data source, such as a bean property. Unlike JSP EL expressions, JavaServer Faces EL expressions are evaluated by the JavaServer Faces implementation rather than by the Web container.

74.What is JavaServer Faces navigation model ?

A mechanism for defining the sequence in which pages in a JavaServer Faces application are displayed.

75.What is HTTPS ?

HTTP layered over the SSL protocol.

76.What is IDL ?

Interface Definition Language. A language used to define interfaces to remote CORBA objects. The interfaces are independent of operating systems and programming languages.

77.What is HTML ?

Hypertext Markup Language. A markup language for hypertext documents on the Internet. HTML enables the embedding of images, sounds, video streams, form fields, references to other objects with URLs, and basic text formatting.

78.What is HTTP ?

Hypertext Transfer Protocol. The Internet protocol used to retrieve hypertext objects from remote hosts. HTTP messages consist of requests from client to server and responses from server to client.

79.What is IIOP ?

Internet Inter-ORB Protocol. A protocol used for communication between CORBA object request brokers.

80.What is ISO 3166 ?

The international standard for country codes maintained by the International Organization for Standardization (ISO).

81.What is ISV ?

Independent software vendor.

82.What is J2EE ?

Java 2 Platform, Enterprise Edition.

83.What is impersonation ?

An act whereby one entity assumes the identity and privileges of another entity without restrictions and without any indication visible to the recipients of the impersonator's calls that delegation has taken place. Impersonation is a case of simple delegation.

84.What is initialization parameter ?

A parameter that initializes the context associated with a servlet.

85.What is J2EE application ?

Any deployable unit of J2EE functionality. This can be a single J2EE module or a group of modules packaged into an EAR file along with a J2EE application deployment descriptor. J2EE applications are typically engineered to be distributed across multiple computing tiers.

86.What is J2EE product ?

An implementation that conforms to the J2EE platform specification.

87.What is J2EE product provider ?

A vendor that supplies a J2EE product.

88.What is J2EE server ?

The runtime portion of a J2EE product. A J2EE server provides EJB or Web containers or both.

89.What is J2EE component ?

A self-contained functional software unit supported by a container and configurable at deployment time. The J2EE specification defines the following J2EE components: Application clients and applets are components that run on the client. Java servlet and JavaServer Pages (JSP) technology components are Web components that run on the server. Enterprise JavaBeans (EJB) components (enterprise beans) are business components that run on the server. J2EE components are written in the Java programming language and are compiled in the same way as any program in the language. The difference between J2EE components and "standard" Java classes is that J2EE components are assembled into a J2EE application, verified to be well formed and in compliance with the J2EE specification, and deployed to production, where they are run and managed by the J2EE server or client container.

90.What is J2EE module ?

A software unit that consists of one or more J2EE components of the same container type and one deployment descriptor of that type. There are four types of modules: EJB, Web, application client, and resource adapter. Modules can be deployed as stand-alone units or can be assembled into a J2EE application.

91.What is J2ME ?

Abbreviate of Java 2 Platform, Micro Edition.

92.What is EAR file ?

Enterprise Archive file. A JAR archive that contains a J2EE application.

93.What is EJB container ?

A container that implements the EJB component contract of the J2EE architecture. This contract specifies a runtime environment for enterprise beans that includes security, concurrency, life-cycle management, transactions, deployment, naming, and other services. An EJB container is provided by an EJB or J2EE server.

94.What is EJB container provider ?

A vendor that supplies an EJB container.

95.What is EJB context ?

A vendor that supplies an EJB container. An object that allows an enterprise bean to invoke services provided by the container and to obtain the information about the caller of a client-invoked method.

96.What is ebXML ?

Electronic Business XML. A group of specifications designed to enable enterprises to conduct business through the exchange of XML-based messages. It is sponsored by OASIS and the United Nations Centre for the Facilitation of Procedures and Practices in Administration, Commerce and Transport (U.N./CEFACT).

97.What is EJB ?

Enterprise JavaBeans.

98.What is EJB Home object ?

An object that provides the life-cycle operations (create, remove, find) for an enterprise bean. The class for the EJB Home object is generated by the container's deployment tools. The EJB Home object implements the enterprise bean's Home interface. The client references an EJB Home object to perform life-cycle operations on an EJB object. The client uses JNDI to locate an EJB Home object.

99.What is EJB JAR file ?

A JAR archive that contains an EJB module.

100.What is enterprise information system resource ?

An entity that provides enterprise information system-specific functionality to its clients. Examples are a record or set of records in a database system, a business object in an enterprise resource planning system, and a transaction program in a transaction processing system.

101.What is Enterprise JavaBeans (EJB) ?

A component architecture for the development and deployment of object-oriented, distributed, enterprise-level applications. Applications written using the Enterprise JavaBeans architecture are scalable, transactional, and secure.

102.What is Enterprise JavaBeans Query Language (EJB QL) ?

Defines the queries for the finder and select methods of an entity bean having container-managed persistence. A subset of SQL92, EJB QL has extensions that allow navigation over the relationships defined in an entity bean's abstract schema.

103.What is EJB server provider ?

A vendor that supplies an EJB server.

104.What is element ?

A unit of XML data, delimited by tags. An XML element can enclose other elements.

105.What is empty tag ?

A tag that does not enclose any content.

106.What is enterprise bean ?

A J2EE component that implements a business task or business entity and is hosted by an EJB container; either an entity bean, a session bean, or a message-driven bean.

107.What is EJB module ?

A deployable unit that consists of one or more enterprise beans and an EJB deployment descriptor.

108.What is EJB object ?

An object whose class implements the enterprise bean's remote interface. A client never references an enterprise bean instance directly; a client always references an EJB object. The class of an EJB object is generated by a container's deployment tools.

109.What is EJB server ?

Software that provides services to an EJB container. For example, an EJB container typically relies on a transaction manager that is part of the EJB server to perform the two-phase commit across all the participating resource managers. The J2EE architecture assumes that an EJB container is hosted by an EJB server from the same vendor, so it does not specify the contract between these two entities. An EJB server can host one or more EJB containers.

110.What is enterprise bean provider ?

An application developer who produces enterprise bean classes, remote and Interview Questions - Home interfaces, and deployment descriptor files, and packages them in an EJB JAR file.

111.What is JMS session ?

A single-threaded context for sending and receiving JMS messages. A JMS session can be nontransacted, locally transacted, or participating in a distributed transaction.

112.What is JSP container ?

A container that provides the same services as a servlet container and an engine that interprets and processes JSP pages into a servlet.

113.What is JSP container, distributed ?

A JSP container that can run a Web application that is tagged as distributable and is spread across multiple Java virtual machines that might be running on different hosts.

114.What is JSP custom action ?

A user-defined action described in a portable manner by a tag library descriptor and imported into a JSP page by a taglib directive. Custom actions are used to encapsulate recurring tasks in writing JSP pages.

115.What is JNDI ?

Abbreviate of Java Naming and Directory Interface.

116.What is JSP ?

Abbreviate of JavaServer Pages.

117.What is JSP custom tag ?

A tag that references a JSP custom action.

118.What is JSP declaration ?

A JSP scripting element that declares methods, variables, or both in a JSP page.

119.What is JSP action ?

A JSP element that can act on implicit objects and other server-side objects or can define new scripting variables. Actions follow the XML syntax for elements, with a start tag, a body, and an end tag; if the body is empty it can also use the empty tag syntax. The tag must use a prefix. There are standard and custom actions.

120.What is JSP directive ?

A JSP element that gives an instruction to the JSP container and is interpreted at translation time.

121.What is JSP document ?

A JSP page written in XML syntax and subject to the constraints of XML documents.

122.What is JSP element ?

A portion of a JSP page that is recognized by a JSP translator. An element can be a directive, an action, or a scripting element.

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