Chapter 8 Introduction to HTML and Applets Fundamentals of Java

2 Objectives Understand the basic features of hypertext, hypermedia, and the World Wide Web. Use basic HTML markup tags to format text for a Web page. Construct an HTML list and an HTML table to represent a linear sequence of items and a two-dimensional grid of items, respectively.

Fundamentals of Java 3 Objectives (cont.) Use the appropriate markup tags to include images in Web pages. Create links to other Web pages using absolute or relative path names. Convert a Java application to an applet and embed the applet in a Web page. Understand the constraints on applets that distinguish them from Java applications.

Fundamentals of Java 4 Vocabulary Absolute path name Associative link Definition list External image Hyperlinks Hypermedia Hypertext

Fundamentals of Java 5 Vocabulary (cont.) Hypertext markup language (HTML) Inline image Markup tag Memex Relative path name Uniform resource locator (URL)

Fundamentals of Java 6 Hypertext, Hypermedia, and the World Wide Web Memex: Theoretical machine proposed by Vannevar Bush in 1945 that would link information in tables by keys – Every computer would have a memex that was linked to the memexes on other computers. – Associative links between computers: Could be traced backwards and forwards

Fundamentals of Java 7 Hypertext, Hypermedia, and the World Wide Web (cont.) Hypertext: A structure consisting of nodes and links between them – Links to other nodes typically displayed to users as embedded, highlighted terms within a given chunk of text Early hypertext systems: – Douglas Englebart’s NLS/Augment (1968) – Cognetics Corporation’s Hyperties (mid-1980s)

Fundamentals of Java 8 Hypertext, Hypermedia, and the World Wide Web (cont.) Hypermedia: Extended hypertext that adds: – GUIs – Images – Sound – Animation – Applications

Fundamentals of Java 9 Hypertext, Hypermedia, and the World Wide Web (cont.) With development of the Internet, people began to think of sharing hypertext across a network of communicating machines. – Each node is a page. – Each page is linked to the World Wide Web. The Web consists of: – Servers: House pages of information – Clients: Run browsers to access information on servers

Fundamentals of Java 10 Hypertext, Hypermedia, and the World Wide Web (cont.) When you view a page in a browser and click on a link: – The browser sends a message to the node’s machine, requesting a transfer of its information. – If the request is successful, the information at the node is downloaded to the user’s browser.

Fundamentals of Java 11 Hypertext, Hypermedia, and the World Wide Web (cont.) Networked hypermedia systems require uniform means of: – Representing data via a machine-independent hypertext markup language – Assigning node addresses using machine- independent uniform resource locators (URLs)

Fundamentals of Java 12 Hypertext, Hypermedia, and the World Wide Web (cont.) Networked hypermedia systems require uniform means of (cont.): – Transmitting information from site to site using machine-independent network transmission protocols – Displaying information with browsers from different vendors

Fundamentals of Java 13 Overview of the Hypertext Markup Language Hypertext markup language (HTML): Machine-independent language for representing information in a networked- based hypermedia system Markup tags: Indicate format of textual elements or links to other nodes

Fundamentals of Java 14 Overview of the Hypertext Markup Language (cont.) Figure 8-1: The Internet

Fundamentals of Java 15 Overview of the Hypertext Markup Language (cont.) Figure 8-2: Simple Web page

Fundamentals of Java 16 Overview of the Hypertext Markup Language (cont.) HTML for the simple Web page:

Fundamentals of Java 17 Overview of the Hypertext Markup Language (cont.) The document must be stored in a file having the extension: – “.html” on a UNIX system – “.htm” on a Windows system Markup tags begin with a left angle bracket ( ). – Not case sensitive

Fundamentals of Java 18 Overview of the Hypertext Markup Language (cont.) Tags often occur in pairs. – Mark the start and end of a tag. – and Tags can include attributes. –

Fundamentals of Java 19 Overview of the Hypertext Markup Language (cont.) Table 8-1: Basic HTML markup tags

Fundamentals of Java 20 Overview of the Hypertext Markup Language (cont.) Minimal document structure:

Fundamentals of Java 21 Overview of the Hypertext Markup Language (cont.) HTML tag: Informs browser that it is dealing with an HTML document HEAD tag: Identifies first part of document TITLE tag: Identifies document’s title – Displayed at top of browser’s window – Used during searches for the document BODY tags: Enclose information provided by the HTML document

Fundamentals of Java 22 Simple Text Elements Headings: Six levels – H1 through H6 – Different font size and style than normal text – Heading Text Paragraphs: Contained within …

Fundamentals of Java 23 Simple Text Elements (cont.) Forced line breaks: tag Preformatted text: Display text “as is” – Contained within … tags

Fundamentals of Java 24 Character-Level Formatting Table 8-2: Some character format tags

Fundamentals of Java 25 Character-Level Formatting (cont.) Escape sequences: Codes to display special characters Table 8-3: Some escape sequences

Fundamentals of Java 26 Lists Unordered (bulleted) lists: Tag Numbered (ordered) lists: Tag Definition (association) lists: Tag For bulleted and ordered lists, use tag for each element in the list. For definition lists, use tag for terms and tag for definitions.

Fundamentals of Java 27 Lists (cont.) Unordered list example: Definition list example:

Fundamentals of Java 28 Lists (cont.) Nested list example:

Fundamentals of Java 29 Lists (cont.) Figure 8-4: Nested list

Fundamentals of Java 30 Linking to Other Documents Links (hyperlinks or hypertext references): Allow readers to move to other pages in the Web – Anchor tag: – Can appear anywhere within any html document – Hyperlinked text is highlighted in some way when displayed: Underlined or a different color, or both

Fundamentals of Java 31 Linking to Other Documents (cont.) Steps to place a link in a document: – 1. Identify target document that will be at link’s other end. Path name or URL – 2. Determine text that labels the link in the browser. – 3. Place this information within an anchor. text of link

Fundamentals of Java 32 Linking to Other Documents (cont.) Path names: – Absolute path name: Specifies exact position of the file in the computer’s directory structure – Relative path name: Specifies a document’s position relative to that of the currently displayed document Uniform resource locator (URL): Used to specify files on another computer – name/document path name

Fundamentals of Java 33 Linking to Other Documents (cont.) Table 8-4: Relative path names to MyPage.html

Fundamentals of Java 34 Multimedia Inline images: Displayed when user opens a page – – Images can be in GIF or JPEG format. – Size attributes: – Alignment attribute:

Fundamentals of Java 35 Multimedia (cont.) External images: Not displayed until user clicks on a link – Use the anchor tag – Sample picture Colors and backgrounds: String of three, two-digit hexadecimal numbers specifies a color by indicating RGB value.

Fundamentals of Java 36 Multimedia (cont.) Table 8-5: Some hypermedia filename extensions

Fundamentals of Java 37 Tables Figure 8-8: A table

Fundamentals of Java 38 Tables (cont.) Table 8-6: Table format tags

Fundamentals of Java 39 Tables (cont.) Table 8-7: Table attributes

Fundamentals of Java 40 Tables (cont.) Typical table format:

Fundamentals of Java 41 Applets A Java application that runs in a Web page – Two components necessary: HTML document that contains an applet markup tag Byte code file for the applet An applet markup tag has the following form: – Applets present a graphical user interface.

Fundamentals of Java 42 Applets (cont.) Figure 8-9: Applet within a Web page

Fundamentals of Java 43 Applets (cont.) HTML code:

Fundamentals of Java 44 Applets (cont.) Converting a Java application to an applet: – Replace the name JFrame with the name JApplet at the beginning of the class definition (extends JApplet ). – Replace constructor by the method init :

Fundamentals of Java 45 Applets (cont.) Example 8.2: Applet with a specialized panel

Fundamentals of Java 46 Applets (cont.) Sun’s applet viewer: Allows programmer to run an applet and view just its GUI – Without the surrounding Web page – Steps to use applet viewer: Compile the Java source program as usual. Create HTML file with at least the minimal applet tag for the applet. At the command line prompt, run appletviewer.

Fundamentals of Java 47 Applets (cont.) Constraints on applets: – Cannot access local files – Byte code file and html file should be in same directory. – Dialog boxes may appear differently. Loading images into an applet:

Fundamentals of Java 48 Applets (cont.) Passing parameters to applets: – Example HTML: Accessing the parameter from the applet class:

Fundamentals of Java 49 Summary The World Wide Web is a hypermedia system that allows users to navigate among and use resources in a nonlinear manner. HTML tags can format text for Web pages. Links to other pages using absolute or relative path names can be included in HTML elements.

Fundamentals of Java 50 Summary (cont.) Web pages can contain applets or Java applications that are downloaded from a Web server and run in the user’s Web browser. A few steps are needed to convert an application to an applet. Applets have most of the functionality of applications, including the GUI, but they lack file access to the user’s disks.