Comp210 Lab 14: HTML and Applets

Table of Contents

Your Web Page

Now, go view your home page! You can edit your new index.html file at your leisure.

Design and layout of your web page is easy to write, but difficult to write well. As you browse other people's pages, pay attention to what makes those pages good or bad. (Does your eye get lost in clutter, or does it glide over the information, recognizing how the page is arranged w/o even being aware of it?)

Some ways to learn about HTML include

• A good on-line introduction to learning HTML.
• Grabbing Owlnet's short documents on beginning HTML and intermediate HTML from Mudd, nextdoor.
• Finding somebody's web page which does something interesting and effectively, and discovering how it's accomplished by pulling down the View menu and choose "Document Source" (this is for Netscape; other browsers have similar features).

Events

An event is some happening outside of the program's control, which the program may be interested in. A few examples are

• mouse events, which include pressing a mouse button down, releasing a mouse button, and even just moving a mouse is an event.
• keypresses, which includes pressing a key down or
• and changing a window on the screen: resizing, uncovering, and moving could all be separate events.

Having a Being event-driven means

In Java, there is a class Applet, which has methods (with names like mouseDown) for various groups of events. When an event occurs, Java repsonds by calling the appropriate method of Applet (such as mouseDown or ), passing arguments to the method which contain details of the event (such as which mouse button or key was pressed down). To make your own applet, just create a class which extends Applet, and then override the methods of the events you'd like to handle.

public class MyZerothApplet extends Applet {
  public boolean mouseDown( Event e, int x, int y ) {
    // Hey!  This is my very own code, being run when a mouse button is clicked!
    // x and y are the coordinates of the click, and e contains
    // further details of the event (e.g. which mouse button).
    System.out.println( "Saw a click-down at (" + x + ", " + y ")." );

    // i've handled the event, so return "true, nobody else needs to
    // worry about doing anything more with the click".
    return true;
    }
  }

Putting Applets into Your Web Page

1. You need to get a certain file in your ~/.netscape directory.

       owl%   ln -s  ~comp210/.netscape/java_301  ~/.netscape
   

   ln -s is conceptually similar to cp, but it just makes a symbolic link--a small pointer to the real file. (In the MacOS, symbolic links are called "aliases".) Good thing, since the real file is 7Meg of java libraries!
2. Quit your current netscape, and instead run netscape3.01 (which is coming from ~comp210/bin, by the way, and it not guaranteed to always be there for you).
3. Inside netscape3.01, from the Options menu select "Network Preferences", thumb to the "Languages" tab, and click the "Enable Java" button.

Example Applets

Example 4-1

Example 4-2

Example 4-3

Example 4-4

Example 4-5

Example 4-6

Example 4-7

Example 4-8

Example 4-10