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J2EE interview questions

Category: JAVA Questions    |    2 views    |    Add a Comment

    1. What makes J2EE suitable for distributed multitiered Applications?
      - The J2EE platform uses a multitiered distributed application model. Application logic is divided into components according to function, and the various application components that make up a J2EE application are installed on different machines depending on the tier in the multitiered J2EE environment to which the application component belongs. The J2EE application parts are:
    2. Client-tier components run on the client machine.
    • Web-tier components run on the J2EE server.
    • Business-tier components run on the J2EE server.
    • Enterprise information system (EIS)-tier software runs on the EIS server.

    1. 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 multitiered, web-based applications.
    2. 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:
    3. Application clients and applets are client components.
    4. Java Servlet and JavaServer Pages technology components are web components.
    5. Enterprise JavaBeans components (enterprise beans) are business components.
    6. Resource adapter components provided by EIS and tool vendors.
    7. What do Enterprise JavaBeans components contain? - Enterprise JavaBeans components contains Business code, which is logic
      that solves or meets the needs of a particular business domain such as banking, retail, or finance, is handled by enterprise beans running in the business tier. All the business code is contained inside an Enterprise Bean which receives data from client programs, processes it (if necessary), and sends it to the enterprise information system tier for storage. An enterprise bean also retrieves data from storage, processes it (if necessary), and sends it back to the client program.
    8. Is J2EE application only a web-based? - No, It depends on type of application that client wants. A J2EE application can be web-based or non-web-based. if an application client executes on the client machine, it is a non-web-based J2EE application. The J2EE application can provide a way for users to handle tasks such as J2EE system or application administration. It typically has a graphical user interface created from Swing or AWT APIs, or a command-line interface. When user request, it can open an HTTP connection to establish communication with a servlet running in the web tier.
    9. Are JavaBeans J2EE components? - No. JavaBeans components are not considered J2EE components by the J2EE specification. They are written to manage the data flow between an application client or applet and components running on the J2EE server or between server components and a database. JavaBeans components written for the J2EE platform have instance variables and get and set methods for accessing the data in the instance variables. JavaBeans components used in this way are typically simple in design and implementation, but should conform to the naming and design conventions outlined in the JavaBeans component architecture.
    10. Is HTML page a web component? - No. Static HTML pages and applets are bundled with web components during application assembly, but are not considered web components by the J2EE specification. Even the server-side utility classes are not considered web components, either.
    11. What can be considered as a web component? - J2EE Web components can be either servlets or JSP pages. Servlets are Java programming language classes that dynamically process requests and construct responses. JSP pages are text-based documents that execute as servlets but allow a more natural approach to creating static content.
    12. What is the container? - Containers are the interface between a component and the low-level platform specific functionality that supports the component. Before a Web, enterprise bean, or application client component can be executed, it must be assembled into a J2EE application and deployed into its container.
    13. What are container services? - A container is a runtime support of a system-level entity. Containers provide components with services such as lifecycle management, security, deployment, and threading.
    14. What is the web container? - Servlet and JSP containers are collectively referred to as Web containers. It manages the execution of JSP page and servlet components for J2EE applications. Web components and their container run on the J2EE server.
    15. What is Enterprise JavaBeans (EJB) container? - It manages the execution of enterprise beans for J2EE applications.
      Enterprise beans and their container run on the J2EE server.
    16. What is Applet container? - IManages the execution of applets. Consists of a Web browser and Java Plugin running on the client together.
    17. How do we package J2EE components? - J2EE components are packaged separately and bundled into a J2EE application for deployment. Each component, its related files such as GIF and HTML files or server-side utility classes, and a deployment descriptor are assembled into a module and added to the J2EE application. A J2EE application is composed of one or more enterprise bean,Web, or application client component modules. The final enterprise solution can use one J2EE application or be made up of two or more J2EE applications, depending on design requirements. A J2EE application and each of its modules has its own deployment descriptor. A deployment descriptor is an XML document with an .xml extension that describes a component’s deployment settings.
    18. What is a thin client? - A thin client is a lightweight interface to the application that does not have such operations like query databases, execute complex business rules, or connect to legacy applications.
    1. What are types of J2EE clients? - Following are the types of J2EE clients:
    2. Applets
    • Application clients
    • Java Web Start-enabled rich clients, powered by Java Web Start technology.
    • Wireless clients, based on Mobile Information Device Profile (MIDP) technology.
    1. What is deployment descriptor? - A deployment descriptor is an Extensible Markup Language (XML) text-based file with an .xml extension that describes a component’s deployment settings. A J2EE application and each of its modules has its own deployment descriptor. For example, an enterprise bean module deployment descriptor declares transaction attributes and security authorizations
      for an enterprise bean. Because deployment descriptor information is declarative, it can be changed without modifying the bean source code. At run time, the J2EE server reads the deployment descriptor and acts upon the component accordingly.
    2. What is the EAR file? - An EAR file is a standard JAR file with an .ear extension, named from Enterprise ARchive file. A J2EE application with all of its modules is delivered in EAR file.
    3. What is JTA and JTS? - JTA is the abbreviation for the Java Transaction API. JTS is the abbreviation for the Jave Transaction Service. JTA provides a standard interface and allows you to demarcate transactions in a manner that is independent of the transaction manager implementation. The J2EE SDK implements the transaction manager with JTS. But your code doesn’t call the JTS methods directly. Instead, it invokes the JTA methods, which then call the lower-level JTS routines. Therefore, JTA is a high level transaction interface that your application uses to control transaction. and JTS is a low level transaction interface and ejb uses behind the scenes (client code doesn’t directly interact with JTS. It is based on object transaction service(OTS) which is part of CORBA.
    4. What is JAXP? - JAXP stands for Java API for XML. XML is a language for representing and describing text-based data which can be read and handled by any program or tool that uses XML APIs. It provides standard services to determine the type of an arbitrary piece of data, encapsulate access to it, discover the operations available on it, and create the appropriate JavaBeans component to perform those operations.
    5. What is J2EE Connector? - The J2EE Connector API is used by J2EE tools vendors and system integrators to create resource adapters that support access to enterprise information systems that can be plugged into any J2EE product. Each type of database or EIS has a different resource adapter. Note: A resource adapter is a software component that allows J2EE application components to access and interact with the underlying resource manager. Because a resource adapter is specific to its resource manager, there is typically a different resource adapter for each type of database or enterprise information system.
    6. What is JAAP? - The Java Authentication and Authorization Service (JAAS) provides a way for a J2EE application to authenticate and authorize a specific user or group of users to run it. It is a standard Pluggable Authentication Module (PAM) framework that extends the Java 2 platform security architecture to support user-based authorization.
    7. What is Java Naming and Directory Service? - The JNDI provides naming and directory functionality. It provides applications with methods for performing standard directory operations, such as associating attributes with objects and searching for objects using their attributes. Using JNDI, a J2EE application can store and retrieve any type of named Java object. Because JNDI is independent of any specific implementations, applications can use JNDI to access multiple naming and directory services, including existing naming and
      directory services such as LDAP, NDS, DNS, and NIS.
    8. What is Struts? - A Web page development framework. Struts combines Java Servlets, Java Server Pages, custom tags, and message resources into a unified framework. It is a cooperative, synergistic platform, suitable for development teams, independent developers, and everyone between.
    9. How is the MVC design pattern used in Struts framework? - In the MVC design pattern, application flow is mediated by a central Controller. The Controller delegates requests to an appropriate handler. The handlers are tied to a Model, and each handler acts as an adapter between the request and the Model. The Model represents, or encapsulates, an application’s business logic or state. Control is usually then forwarded back through the Controller to the appropriate View. The forwarding can be determined by consulting a set of mappings, usually loaded from a database or configuration file. This provides a loose coupling between the View and Model, which can make an application significantly easier to create and maintain. Controller: Servlet controller which supplied by Struts itself; View: what you can see on the screen, a JSP page and presentation components; Model: System state and a business logic JavaBeans.

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    Java GUI designer interview questions

    Category: JAVA Questions    |    31 views    |    1 Comment

    1. What advantage do Java’s layout managers provide over traditional windowing systems? - Java uses layout managers to lay out components in a consistent manner across all windowing platforms. Since Java’s layout managers aren’t tied to absolute sizing and positioning, they are able to accomodate platform-specific differences among windowing systems.
    2. What is the difference between the paint() and repaint() methods? - The paint() method supports painting via a Graphics object. The repaint() method is used to cause paint() to be invoked by the AWT painting thread.
    3. How can the Checkbox class be used to create a radio button? - By associating Checkbox objects with a CheckboxGroup
    4. What is the difference between a Choice and a List? - A Choice is displayed in a compact form that requires you to pull it down to see the list of available choices. Only one item may be selected from a Choice. A List may be displayed in such a way that several List items are visible. A List supports the selection of one or more List items.
    5. What interface is extended by AWT event listeners? - All AWT event listeners extend the java.util.EventListener interface.
    6. What is a layout manager? - A layout manager is an object that is used to organize components in a container
    7. Which Component subclass is used for drawing and painting? - Canvas
    8. What are the problems faced by Java programmers who dont use layout managers? - Without layout managers, Java programmers are faced with determining how their GUI will be displayed across multiple windowing systems and finding a common sizing and positioning that will work within the constraints imposed by each windowing system
    9. What is the difference between a Scrollbar and a ScrollPane? (Swing) - A Scrollbar is a Component, but not a Container. A ScrollPane is a Container. A ScrollPane handles its own events and performs its own scrolling.

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    Java interview questions

    Category: JAVA Questions    |    1 views    |    Add a Comment

    1. What is the Collections API? - The Collections API is a set of classes and interfaces that support operations on collections of objects
    2. What is the List interface? - The List interface provides support for ordered collections of objects.
    3. What is the Vector class? - The Vector class provides the capability to implement a growable array of objects
    4. What is an Iterator interface? - The Iterator interface is used to step through the elements of a Collection
    5. Which java.util classes and interfaces support event handling? - The EventObject class and the EventListener interface support event processing
    6. What is the GregorianCalendar class? - The GregorianCalendar provides support for traditional Western calendars
    7. What is the Locale class? - The Locale class is used to tailor program output to the conventions of a particular geographic, political, or cultural region
    8. What is the SimpleTimeZone class? - The SimpleTimeZone class provides support for a Gregorian calendar
    9. What is the Map interface? - The Map interface replaces the JDK 1.1 Dictionary class and is used associate keys with values
    10. What is the highest-level event class of the event-delegation model? - The java.util.EventObject class is the highest-level class in the event-delegation class hierarchy
    11. What is the Collection interface? - The Collection interface provides support for the implementation of a mathematical bag - an unordered collection of objects that may contain duplicates
    12. What is the Set interface? - The Set interface provides methods for accessing the elements of a finite mathematical set. Sets do not allow duplicate elements
    13. What is the purpose of the enableEvents() method? - The enableEvents() method is used to enable an event for a particular object. Normally, an event is enabled when a listener is added to an object for a particular event. The enableEvents() method is used by objects that handle events by overriding their event-dispatch methods.
    14. What is the ResourceBundle class? - The ResourceBundle class is used to store locale-specific resources that can be loaded by a program to tailor the program’s appearance to the particular locale in which it is being run.
    15. What is the difference between yielding and sleeping? - When a task invokes its yield() method, it returns to the ready state. When a task invokes its sleep() method, it returns to the waiting state.
    16. When a thread blocks on I/O, what state does it enter? - A thread enters the waiting state when it blocks on I/O.
    17. When a thread is created and started, what is its initial state? - A thread is in the ready state after it has been created and started.
    18. What invokes a thread’s run() method? - After a thread is started, via its start() method or that of the Thread class, the JVM invokes the thread’s run() method when the thread is initially executed.
    19. What method is invoked to cause an object to begin executing as a separate thread? - The start() method of the Thread class is invoked to cause an object to begin executing as a separate thread.
    20. What is the purpose of the wait(), notify(), and notifyAll() methods? - The wait(),notify(), and notifyAll() methods are used to provide an efficient way for threads to wait for a shared resource. When a thread executes an object’s wait() method, it enters the waiting state. It only enters the ready state after another thread invokes the object’s notify() or notifyAll() methods.
    21. What are the high-level thread states? - The high-level thread states are ready, running, waiting, and dead
    22. What happens when a thread cannot acquire a lock on an object? - If a thread attempts to execute a synchronized method or synchronized statement and is unable to acquire an object’s lock, it enters the waiting state until the lock becomes available.
    23. How does multithreading take place on a computer with a single CPU? - The operating system’s task scheduler allocates execution time to multiple tasks. By quickly switching between executing tasks, it creates the impression that tasks execute sequentially.
    24. What happens when you invoke a thread’s interrupt method while it is sleeping or waiting? - When a task’s interrupt() method is executed, the task enters the ready state. The next time the task enters the running state, an InterruptedException is thrown.
    25. What state is a thread in when it is executing? - An executing thread is in the running state
    26. What are three ways in which a thread can enter the waiting state? - A thread can enter the waiting state by invoking its sleep() method, by blocking on I/O, by unsuccessfully attempting to acquire an object’s lock, or by invoking an object’s wait() method. It can also enter the waiting state by invoking its (deprecated) suspend() method.
    27. What method must be implemented by all threads? - All tasks must implement the run() method, whether they are a subclass of Thread or implement the Runnable interface.
    28. What are the two basic ways in which classes that can be run as threads may be defined? - A thread class may be declared as a subclass of Thread, or it may implement the Runnable interface.
    29. How can you store international / Unicode characters into a cookie? - One way is, before storing the cookie URLEncode it. URLEnocder.encoder(str); And use URLDecoder.decode(str) when you get the stored cookie.

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    Common JSP interview questions

    Category: JAVA Questions    |    1 views    |    Add a Comment

    1. What are the implicit objects? - Implicit objects are objects that are created by the web container and contain information related to a particular request, page, or application. They are: request, response, pageContext, session, application, out, config, page, exception.
    2. Is JSP technology extensible? - Yes. JSP technology is extensible through the development of custom actions, or tags, which are encapsulated in tag libraries.
    3. How can I implement a thread-safe JSP page? What are the advantages and Disadvantages of using it? - You can make your JSPs thread-safe by having them implement the SingleThreadModel interface. This is done by adding the directive <%@ page isThreadSafe=”false” %> within your JSP page. With this, instead of a single instance of the servlet generated for your JSP page loaded in memory, you will have N instances of the servlet loaded and initialized, with the service method of each instance effectively synchronized. You can typically control the number of instances (N) that are instantiated for all servlets implementing SingleThreadModel through the admin screen for your JSP engine. More importantly, avoid using the tag for variables. If you do use this tag, then you should set isThreadSafe to true, as mentioned above. Otherwise, all requests to that page will access those variables, causing a nasty race condition. SingleThreadModel is not recommended for normal use. There are many pitfalls, including the example above of not being able to use <%! %>. You should try really hard to make them thread-safe the old fashioned way: by making them thread-safe
    4. How does JSP handle run-time exceptions? - You can use the errorPage attribute of the page directive to have uncaught run-time exceptions automatically forwarded to an error processing page. For example: <%@ page errorPage=”error.jsp” %>
      redirects the browser to the JSP page error.jsp if an uncaught exception is encountered during request processing. Within error.jsp, if you indicate that it is an error-processing page, via the directive: <%@ page isErrorPage=”true” %> Throwable object describing the exception may be accessed within the error page via the exception implicit object. Note: You must always use a relative URL as the value for the errorPage attribute.
    1. How do I prevent the output of my JSP or Servlet pages from being cached by the browser? - You will need to set the appropriate HTTP header attributes to prevent the dynamic content output by the JSP page from being cached by the browser. Just execute the following scriptlet at the beginning of your JSP pages to prevent them from being cached at the browser. You need both the statements to take care of some of the older browser versions.
    2. <%
      response.setHeader(”Cache-Control”,”no-store”); //HTTP 1.1

      response.setHeader(”Pragma”,”no-cache”); //HTTP 1.0

      response.setDateHeader (”Expires”, 0); //prevents caching at the proxy
      server
      %>

    

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