chapter 8 introduction to html and applets fundamentals of java
TRANSCRIPT
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.
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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.
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Vocabulary
Absolute path name Associative link Definition list External image Hyperlinks Hypermedia Hypertext
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Vocabulary (cont.)
Hypertext markup language (HTML) Inline image Markup tag Memex Relative path name Uniform resource locator (URL)
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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
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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)
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Hypertext, Hypermedia, and the World Wide Web (cont.)
Hypermedia: Extended hypertext that adds:– GUIs– Images– Sound– Animation– Applications
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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
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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.
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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)
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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
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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
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Overview of the Hypertext Markup Language (cont.)
Figure 8-2: Simple Web page
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Overview of the Hypertext Markup Language (cont.)
HTML for the simple Web page:
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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 (<) and end with a right angle bracket (>).– Not case sensitive
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Overview of the Hypertext Markup Language (cont.)
Tags often occur in pairs.– Mark the start and end of a tag.– <TITLE> and </TITLE>
Tags can include attributes.– <P ALIGN=CENTER>
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Overview of the Hypertext Markup Language (cont.)
Table 8-1: Basic HTML markup tags
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Overview of the Hypertext Markup Language (cont.)
Minimal document structure:
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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
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Simple Text Elements
Headings: Six levels– H1 through H6– Different font size and style than normal text– <Hnumber>Heading Text</Hnumber>
Paragraphs: Contained within <P>…</P>
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Simple Text Elements (cont.)
Forced line breaks: <br> tag Preformatted text: Display text “as is”
– Contained within <Pre>…</Pre> tags
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Character-Level Formatting (cont.)
Escape sequences: Codes to display special characters
Table 8-3: Some escape sequences
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Lists
Unordered (bulleted) lists: Tag <UL> Numbered (ordered) lists: Tag <OL> Definition (association) lists: Tag <DL> For bulleted and ordered lists, use <LI> tag
for each element in the list. For definition lists, use <DT> tag for terms
and <DD> tag for definitions.
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Linking to Other Documents
Links (hyperlinks or hypertext references): Allow readers to move to other pages in the Web– Anchor tag: <A>– Can appear anywhere within any html
document– Hyperlinked text is highlighted in some way
when displayed:Underlined or a different color, or both
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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.<A HREF="target document identifier">text of link</A>
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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– http://server name/document path name
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Linking to Other Documents (cont.)
Table 8-4: Relative path names to MyPage.html
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Multimedia
Inline images: Displayed when user opens a page– <IMG SRC="ImageLocation">– Images can be in GIF or JPEG format.– Size attributes:
<IMG SRC="mypicture.gif" HEIGHT=100 WIDTH=100>
– Alignment attribute:<IMG SRC="mypicture.gif" ALIGN=CENTER>
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Multimedia (cont.)
External images: Not displayed until user clicks on a link– Use the anchor tag– <A HREF="mypicture.gif">Sample picture</A>
Colors and backgrounds: String of three, two-digit hexadecimal numbers specifies a color by indicating RGB value.
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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:– <APPLET CODE="byte code file name" WIDTH=width HEIGHT=height></APPLET>
Applets present a graphical user interface.
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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:
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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 <html file name>.
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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:
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Applets (cont.)
Passing parameters to applets:– Example HTML:
Accessing the parameter from the applet class:
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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.
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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.