Java FAQ

  1. Introduction to Java
    Java is an object-oriented programming language developed by Sun Microsystems.When Programmers compile a java program, the resulting object code typically is called bytecode, which is machine independent.Java then uses a just-in-time (JIT) compiler to convert the bytecode into machine-dependent code that is executed immediately.Programmers use Java Platform, standard Edition (Java SE), developed by Sun Microsystems, to create stand-alone programs for desktop computers and servers.
    Similarly, programmers use Java Platform, micro Edition (java ME) to create phones and other mobile devices.
    Java EE (Java Platfprm Enterprise Edition) is a set of technologies built on Sun's Java SE that allows programmers to develop and deploy large applications for organizations often used in web 2.0 environment for web applications.
    The goal of java EE is to simplify and reduce program development time by developing standard,reusable objects.
  2. What is Web 2.0?
    It refers to web sites that provide a means for users to share personal information, allow users to modify web site content, and have application software built into the site for visitors to use.Web 2.0 Sites include social networking sites,wikis,blogs,online auctions, and web applications such as Google Docs.
    Most web 2.0 Sites also use APIs so that Web Developers can create their own web applications.An API (application programming interface) is a collection of tools that programmers use to interact with an environment such as a web site or operating system.
    Mapping web sites, for example ,include APIs that enable programmers to integrate maps into their web sites.Another use of API is the mashups. A mashup is a web application that combines services from two or more sources, creating a new application.
  3. What are run-time errors?
    Say you forget a closing curly brace in your java code. This will result in compilation error that can be fixed easily.But there are so called run-time errors, when all of a sudden your program stops working properly. Run-time errors in java are called exceptions, and error processing is called exception handling.A method throws an exception in case of an error. different exceptions will be thrown for different type of errors.
  4. What is an Exceptional handling mechanism ?
    Java Provides an exception-handling mechanism that helps us build robust code. When an error occurs at runtime, an exception is thrown. It is possible for an application to catch this exception and in many cases, recover from it.
  5. what is called stack trace?.
    If an unexpected exception occurs that is not handled by the program, it prints a multiline error message on the screen. such message is called stack trace.
  6. Whar are the five keywords that can be used for error handling?
    try,catch,finally,throw and throws.After one try block we may put several catch blocks. If we write several catch blocks, we may need to place them in a particular order if these exceptions are inherited from each other.For Example , Since the EOFException is a subclass of the IOException. We have to put the catch block for the subclass first. If we would put the catch for IOException first, the program would never reach the FileNotFound or EOFException because the first catch would intercept them. Catch blocks receive an instance of the object Exception that contains a short explanation of a problem, and its method getMessage() will return this info.Sometimes, if the description of an error is not clear,try the method toString() instead.
    if we need more detailed information about the exception , use the method printStackTrace().
    In some cases , it makes more sense to handle the exception not in the method where it happened, but in the method's caller. In such cases the method signature has to declare(warn) that it may throw a particular exception. This is done using a special keyword throws.

    If a method throws an Exception that it will not catch but that will be caught by a different method.This practice is known as exception specification.
    A throw statement is one that sends an Exception out of a block or a method so it can be handled elsewhere.
  7. Write Short notes About HTML?
    HTML is platform independent, meaning you can create, or code, an HTML file on one type of computer and then use a browser on another type of computer to view that file as a Web page. The page looks the same regardless of what platform you are using.One of the greatest benefits of Web technology is that the same Web page can be viewed on many different types of digital hardware, including mobile devices like smart phones. If you create a Web page in HTML and do not follow XHTML coding standards exactly (for example, by not using an end &lt/p&gt tag), the Web browser on your computer can still interpret and display the Web page correctly. However, newer types of brows-ers, such as those for mobile phones or handheld computers, cannot interpret HTML code that does not meet XHTML standards.
  8. What is the purpose of the alt attribute?
    The alt attribute has three important pur-poses. First, screen readers used by users with visual impair-ments read the alter-nate text out loud. Second, the alter- nate text is displayed while the image is being loaded. Finally, the alt tag is re-quired for XHTML compliance.
  9. What is the purpose of the < div > and </ div > tags?
    The < div > tag establishes a division within a Web page. When you use the < div > </ div > tags, you are able to design a layout that uses CSS, including inserting images.
  10. Why am I using the transitional document type? Doesn't that allow the use of deprecated tags?
    Yes, you can use dep-recated tags with a transitional document type. Some valid tags (e.g., name) cannot be used with the XHTML 1.1 standard, so this text uses XHTML 1.0 with the transitional document type.
  11. What is the difference between the < title > and < body > tags?
    The text contained within the < title > </ title > tags is what appears on the browser title bar when the Web page is displayed in the browser window. The text and graphics contained within the < body > </ body > tags are what is displayed in the browser window.
  12. Can I use either uppercase or lowercase letters for my HTML code?
    To make your HTML files compliant with XHTML standards, always enter tags in lowercase (with the exception of the <! DOCTYPE > tag, which is always uppercase).
  13. Why should I include the width, height, and alt attributes?
    Adding width and height attributes can improve page loading time because the browser does not have to figure the width and height before loading the image. Never use the height and width attributes to resize an image, however. Use graphic editing software to resize it and save it with a different file name. The height and width attributes as used in the img tag should rel ect the actual image size. The alt attribute provides information about the purpose of the image when the user's mouse hovers over the image and while the image is loading.
  14. How to Check Your Website?
    Most modern desktop and laptop computers use at least 1024 X 768 pixel resolution, but it's a good idea to check your pages at lower resolutions, such as 800 X 600 pixels and 640 X 480 pixels, given the increasing popularity of small-screened "netbook" computers, handheld computers, and Web-capable mobile phones.
  15. What is the best width of a browser window.?
    A pixel is the smallest unit of measurement on a monitor, and is otherwise known as "dot." For example, a resolu- tion of 1024 X 768 means that a monitor displays a grid of pixels that's 1,024 pixels wide and 768 pixels high (for a total of 786,432 pixels). The smallest resolution you're likely to find today (outside of a mobile phone) is 1024 X 600, which are the dimensions of the typical netbook screen. But remember, people with large monitors won't necessarily size their browser window to fill up the entire screen. (After all, it's hard to read really long lines of text.) For that reason, 1,000 pixels is a good lower-limit assumption you can make for the width of a browser window.
  16. What is Hosting?
    Hosting means placing the files and graphics and such on a Web server.
  17. What is WML?
    WML is a markup language based on XML (Extensible Markup Language). It is designed for specifying user interface behavior and displaying content on wireless devices such as phones, pagers, and PDAs (Personal Digital Assistants).Two versions- WML 2.x and WML 1.x ,WML 2.x includes XHTML-MP which includes XHTML.WML 1.x does not include XHTML
  18. What is Bandwidth?
    Bandwidth (or web traffic, as it's sometimes called) is the maximum amount of information you can deliver to anyone who visits your site in a month. Usually, you can make do with the lowest bandwidth your hosting company offers. You don't need much. In fact, most people can ignore this number altogether. The only exceptions are if your website is absurdly popular; if you want to store extremely large files and let visitors download them; or if you're showcasing a huge catalog of digital photos, music, or video, and you don't want to use a third- party service like Flickr or YouTube. If you are in the small minority of people who needs huge amounts of bandwidth, look for a web host that promises unlimited bandwidth. That way, you don't need to worry about exceeding your limit.
  19. What is FrontPage extensions?
    If you create your site using Expression Web (Microsoft's successor to FrontPage), you can use FrontPage server extensions to get a few extra frills. For example, you can count the number of visitors to a certain page and let visitors upload files to the server.
  20. What is RSS?
    RSS (Really Simple Syndication) is a file format that allows Web sites to easily make their content available to readers, such as yourself. The content is packaged into what is called an RSS feed or RSS channel. To see this content, you subscribe to an RSS feed. Then, you can view the RSS feed using an RSS Reader or an RSS Aggregator.The major Web browsers now have built-in RSS Readers, mak- ing it more convenient than ever to subscribe to and view RSS feeds. And once you've subscribed to an RSS feed, you won't need to go back to the Web site that provides the feed. You can simply open your RSS Reader and view all the most up-to-date content from that site, based on the feed to which you subscribed
  21. What is Ajax?
    Ajax (sometimes written as AJAX) stands for Asynchronous JavaScript and XML. It is a Web- based technique that creates a more seamless user experience when a Web page is updated based on user input. For instance, a page not using Ajax will take user input and submit it to a script on the Web server for processing. This is often the result of the user clicking a submit button or selecting something in a pull-down menu. The user input is then processed by the server, and a new HTML page is created. This new page is returned to the browser, and the existing page is refreshed. A Web page using Ajax also takes user input, and submits it to a script on the Web server. This is triggered in the same manner as above; however, the user input is sent to the Web server differently. The user input is then processed by the server, but instead of creating a new HTML page, only new data is created. This new data is returned to the browser (again via a different mechanism than in the non-Ajax experience). Then, instead of refreshing the page, the existing page is sim- ply updated with the new data. Ajax is not a language. It is a specific way of using existing languages to create a more inter- active Web experience. It is the combination of HTML (used to display the Web page), XML (used to exchange data between the server-side script and the Web page), and JavaScript (used to update the HTML page with new data and bind the entire process together).
  22. What is SOAP and Web Services?
    SOAP stands for Simple Object Access Protocol. (Technically, with version 1.2, that definition was dropped, yet most people still use it any- way.) In either case, SOAP is an XML-based messaging framework. In the same way that a person can request a stock price or an item's inventory from a server, SOAP supports server- to-server communication. Specifically, it allows for platform- and language-independent com- munication between different applications, typically running on different servers. SOAP's support of this type of interoperabil- ity has made it an important part of what the W3C calls a Web Service. A Web Service is a set of functions that can be accessed and executed over a network. While generic in its definition, a Web Service usually refers to the exchange of XML messages using the SOAP framework. SOAP's core functionality is to support this exchange of XML messages from one applica- tion to another. SOAP is a lightweight protocol because, for the most part, a SOAP message is basically an XML file in a SOAP wrapper. And, this wrapper, often referred to as the SOAP envelope , adds very little over- head to the messaging process. The exchange of SOAP messages is most fre- quently done over the Internet via HTTP. A client application sends a SOAP message as an HTTP request, and the server sends back its SOAP message as an HTTP response. Because the SOAP message exchange works using HTTP, it allows for easier communica- tion between computers on different networks than was previously possible. This is one of the biggest advantages of using SOAP over other remote communication frameworks.
  23. What is XML?
    XML, or eXtensible Markup Language, is a specification for storing information. It is also a specification for describing the structure of that information. And while XML is a markup language (just like HTML), XML has no tags of its own. It allows the person writing the XML to create whatever tags they need. The only condition is that these newly created tags adhere to the rules of the XML specification.
  24. What is XSLT?
    The details for formatting XML documents was originally in a specifica- tion called XSL, which stands for eXtensible Style Language. However, because it was taking so long to finish, the W3C divided XSL into two pieces: XSLT (for Transformations) and XSL-FO (for Formatting Objects). The end result might be another XML document or an HTML document. In real- ity, you can transform an XML document into practically any document type you like. Transforming an XML document means using XSLT to analyze its contents and then take certain actions depending on what elements are found. You can use XSLT to reorder the output according to specific criteria, display only cer- tain pieces of information, and much more. XSL-FO is typically used to format XML for print output, such as going directly to a PDF. It is not supported by any browsers, and requires specific parsing software to use.
  25. What is KML?
    KML (Keyhole Markup Language) is an XML markup language for annotating maps using placemarks, polygonal shapes, paths, descrip- tions, and the like. It was initially developed for use with Google Earth (an application often run on your local computer). Since then, it has been adopted for use by many other map-related applications.
  26. What are Plug-ins,ActiveX Controls,Java Applets ?
    Plug-ins such as the Flash player, QuickTime player, and others, are small helper programs (components) that extend the browser to support new functionality. Plug-ins are primarily a Netscape technology and have been around since Netscape Navigator 2. ActiveX (http://www.microsoft.com/com/tech/activex.asp), which is the Internet portion of the Component Object Model (COM), is Microsoft's component technology for creating small components, or controls, within a Web page. It is intended to distribute these controls via the Internet to add new functionality to browsers such as Internet Explorer. Whereas both Microsoft's ActiveX and Netscape's plug-ins are platform and browser specific, Sun Microsystems' Java technology (http://java.sun.com) aimed to provide a platform-neutral development language, allowing programs to be written once and deployed on any machine, browser, or operating system that supports the Java virtual machine (JVM). Java uses small Java programs, called applets, that were first introduced by Sun's HotJava browser.
  27. What is WS_FTP?
    WS_FTP FTP stands for File Transfer Protocol, a way to transfer files between computers over the Internet. If you have trouble configuring FrontPage to upload pages to a Web server, use an FTP program. Using an FTP program is the most straightforward way to upload a Web site to a Web server. WS_FTP is the most popular FTP program used to upload and download Web pages. The Home version is free to use for 30 days, and can be downloaded at www.ipswitch.com.
  28. What are Secure servers?
    Secure servers offer another layer of security via encrypted data streams between the server and the client. Typically referred to as Secure Socket Layer (SSL), this layer can be implemented on many Internet-enabled applications Web servers,e-mail servers, and so on.Secure servers protect against eavesdroppers, hackers that intercept the communication between the user and server to obtain login information, personal data, credit card information, and so on. Various servers implement SSL in various ways. In each case, you will need a certificate for use with your server. A certificate is an electronic document that is signed by a trusted authority, representing that the owner of the certificate is who they say they are. It's a means of providing ID to users of your site and saying "you can trust me because I am who I say I am." There are quite a few certificate authorities, some more trusted than others. You can even sign your own certificates, though the result isn't worth much for convincing end users to trust you Thawte is a good place to start if you need a signed certificate. (www.thawte .com/)
  29. What are Client-Side versus Server-Side Scripting?
    There are two basic varieties of scripting,client-side and server-side. As their names imply,the main difference is where the scripts are actually executed. Client-side scripts are run by the client software--that is, the user agent. As such, they impose no additional load on the server, but the client must support the scripting language being used. JavaScript is the most popular client-side scripting language, but Jscript and VBScript are also widely used. Client-side scripts are typically embedded in HTML documents and deployed to the client. As such, the client user can usually easily view the scripts. For security reasons, client-side scripts generally cannot read or write to the server or client file system. Server-side scripts are run by the Web server. Typically, these scripts are referred to as CGI scripts, CGI being an acronym for Common Gateway Interface,the first interface for server-side Web scripting. Server-side scripts impose more load on the server, but generally don't influence the client-even output to the client is optional; the client may have no idea that the server is running a script. Perl,Python,PHP,and Java are all examples of server-side scripting languages.The script typically resides only on the server, but is called by code in the HTML document. Although server-side scripts cannot read or write to the client's file system, they usually have some access to the server's file system. As such, it is important that the system administrator take appropriate measures to secure server-side scripts and limit their access.
  30. Why fireworks ?
    Fireworks is an ideal choice for creating Web graphics because after you finish building your graphics, you can easily add links, rollover buttons, and even drop-down menus without needing to write any code. When you export your Fireworks file, you get not only the graphics, but also the HTML page that makes it all work. Photoshop does have the ability to slice and optimize Web graphics, but it cannot add interactivity like this to the exported HTML page.
  31. What is Streaming media ?
    Although video and audio can add a lot of life to your Web site, they can be cumbersome for users to download. While many people have fast home DSL connections, many users today still access the Internet via their phone line and their computer's internal modem. The speed of these internal modems is usually 56,000 bits (56K) per second-meaning that they can download only 56K worth of data each second. If you consider that a Web page with media like a QuickTime movie can add up to one megabyte (which translates to 8,000,000 bits), the page would take nearly 21/2 minutes to download. That's almost the same time it takes to sit through a TV commercial break. To get around the problem of inadequate bandwidth, video and audio for the Web are prepared such that they stream in instead of download. Streaming media downloads in chunks so that people can start watching or listening almost immediately to the first chunk while the rest of the chunks download. Working with and preparing streaming media is similar to preparing other media, such as graphics, for the Web. You must compress and save it in a Web-friendly format. This process is called encoding and involves selecting a combination of file format and codec (short for compressor/de-compressor). Sometimes the two are inextricably linked as in the case of Real Video and Windows Media-both of which are formats with their own proprietary codecs. For optimal Web delivery, you must encode video and audio media with a target bandwidth in mind (like DSL or 56K). The lower the connection speed, the more compression you need. For even better performance, you can upload the finished files to different servers. If a lot of people look at the same file simultaneously, you don't put undue strain on one server or slow down the media's delivery if the file is distributed.
  32. What is a site map?
    A site map is a set of links to every single page on your website. On larger sites, it's probably the only place where you can get to any page from one spot. If you have fewer than 10 pages, a web page with your site map on it probably isn't necessary (although it can't hurt). Past 10 pages, however, a site map page can be very helpful as a guide for visitors. In particular, it's a great place to link to on your error page (when visitors have tried to get to a page that doesn't exist on your site). And when you do have a great many pages, it can be helpful to have a hierarchical site map. This makes it easier for visitors to see the relationships between pages and not have to hunt through to figure out the section they want.
  33. What are about Vector and Bitmap Images?
    There are two general types of graphics used on the Web: vector and bitmap. Bitmap images, which are mainly comprised of JPGs, PNGs, and GIFs, continue to be the most commonly used type of image on the Internet. The second type of graphics are vector images. These use mathematically based lines and curves to display images, as opposed to bitmap images, which use pixels to display images. A designer could create the same exact image in both a vector-based program, such as Adobe Illustrator, or a bitmap-based program, such as Adobe Photoshop. (More recent versions of Photoshop now also support vector-based images.)
  34. What are page layout options?
    Before building a page layout, there are a few decisions you should make. The first is the width of the layout. There are two main categories of layout widths: fixed-width layouts and flexible layouts. Fixed-width layouts are much more common: in a fixed-width layout, all page elements are nested within a container that has an explicit width.A fixed-width layout is useful for the designer because it offers a way to reliably position the various layout elements (such as headers, sidebars, and footers). It also provides a reliable structure for elements, such as the width of a paragraph on a page or the placement of images. Flexible layouts are so named because they are designed to adapt to the width of the browser window. This style of layout is useful when users have different monitor resolutions, making it impossible to build a fixed-width layout that looks the same on every screen. A properly designed flexible layout can automatically adjust to fit the user's browser window. You could argue that flexible layouts are more appropriate for the web. It is, after all, not print: both text and images on a web page can rel ow. Now that mobile devices make up a substantial proportion of web browsers, a flexible layout might be better suited to these new interfaces than a fixed-width layout. Flexible-width layouts are much more difficult to build. There are more decisions for the designer to make and more options to consider.
  35. What are Positioning models in CSS?
    In addition to absolute and relative positioning, there is a property called fixed positioning, that is used less frequently than the other two. Here is a brief description of each of the properties:

    Absolute positioning: An element that is set to absolute strictly follows the positioning values given to it, relative only to its containing element. The containing element can be another div or the actual page. Absolutely positioned elements are pulled out of the normal flow of HTML content, and regardless of the elements that surround them (such as, text content or neighboring divs), they always appear at the exact coordinates assigned to them.

    Relative positioning: A relatively positioned element accepts values for position properties such as top and left, but it also takes the normal flow of neighboring HTML content into account. For example, a value of left:35 would add 35 pixels to the element's left position.

    Fixed positioning: This property generates an absolutely positioned element that is positioned relative to the browser window. In other words, by fixed positioning an element, you are anchoring it to your browser window. This effect is used for elements such as footers or menus that you want to stay in the same position in the browser window (even when the user scrolls down).
  36. What is web serever ?
    Using the client/server model and the World Wide Web's Hypertext Transfer Protocol (HTTP), serves the files that form Web pages to Web users (whose computers contain HTTP clients that forward their requests). Every computer on the Internet that contains a Web site must have a Web server program. Apache,Tomcat,IIS
  37. What is a gadget or widget?
    A new trend is taking over from cut-and-paste JavaScript sharing, without re- quiring the complexity of a JavaScript library: web widgets. Essentially, a web widget is a self-contained, miniature application that you can pop into one or more web pages. A typical widget fits in a small box on the page, and is pow-ered by JavaScript. Common examples include widgets that show constantly up- dated news headlines, offer interactive games, play music, display slideshows, poll visitors, collect data with forms, and much more. You can search for a widget to call your own at one of the many widget repositories on the Web, such as www.widgetbox.com, www.google.com/ig/directory?synd=open, and www.widgipedia.com.
  38. What is the Hosted Multimedia?
    Hosted multimedia- multimedia files stored on someone else's server but displayed (or linked to) on your web page. The best-known example of hosted multimedia is YouTube, a ridiculously popular site that plays back hundreds of millions of video clips every day. Hosted multimedia is an excellent choice if you want to display really large files, particularly movie clips. It won't tap out your website's bandwidth, and it works with virtually all browsers and operating systems

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