Create the logo as shown in Java in an applet or frame. It should be as close as

Question

Create the logo as shown in Java in an applet or frame. It should be as close as possible, including the Virus Logo. Draw the logo using ovals, lines, rectangles, and strings, changing colors and using draw or fill as necessary. Change to appropriate virus colors (like Blue and Cyan) and fonts for the text in the drawing. Everything should be drawn in paint() with your Graphics object. After creating one virus, usecopyArea() to copy the virus bugs to other areas of the Container.

Document your .java file with five lines at the top and five lines throughout explaining the purpose of the program. Take a picture of your output with <Alt><Ptr>, paste into Paint, and save as a .jpg. Submit both your .java program and .jpg files. Please post the image too

Explanation / Answer

import java.applet.Applet;  

import java.awt.Graphics;

public class HelloWorldApplet extends Applet {

  public void paint(Graphics g) {

    g.drawString("Hello world!", 50, 25);

}

}

The applet version of HelloWorld is a little more complicated than the HelloWorld application, and it will take a little more effort to run it as well.

First type in the source code and save it into file called HelloWorldApplet.java. Compile this file in the usual way. If all is well a file called HelloWorldApplet.class will be created. Now you need to create an HTML file that will include your applet. The following simple HTML file will do.

Save this file as HelloWorldApplet.html in the same directory as the HelloWorldApplet.class file. When you've done that, load the HTML file into a Java enabled browser like Internet Explorer 4.0 or Sun's applet viewer included with the JDK. You should see something like below, though of course the exact details depend on which browser you use.

If you're using the JDK 1.1 to compile your program, you should use the applet viewer, HotJava, Internet Explorer 4.0 or later, or Netscape 4.0.6 or later on Windows and Unix to view the applet. Netscape Navigator 4.0.5 and earlier and 3.x versions of Internet Explorer do not support Java 1.1. Furthermore, no Mac version of Navigator supports Java 1.1.

If the applet compiled without error and produced a HelloWorldApplet.class file, and yet you don't see the string "Hello World" in your browser chances are that the .class file is in the wrong place. Make sure HelloWorldApplet.class is in the same directory as HelloWorld.html. Also make sure that you're using a version of Netscape or Internet Explorer which supports Java. Not all versions do.

In any case Netscape's Java support is less than the perfect so if you have trouble with an applet, the first thing to try is loading it into Sun's Applet Viewer instead. If the Applet Viewer has a problem, then chances are pretty good the problem is with the applet and not with the browser.

What is an Applet?

According to Sun "An applet is a small program that is intended not to be run on its own, but rather to be embedded inside another application....The Applet class provides a standard interface between applets and their environment."

Four definitions of applet:

public class Applet extends Panel

The APPLET HTML Tag

Applets are embedded in web pages using the <APPLET> and </APPLET> tags. The <APPLET> tag is similar to the <IMG> tag. Like <IMG> <APPLET> references a source file that is not part of the HTML page on which it is embedded. IMG elements do this with the SRC attribute. APPLET elements do this with the CODE attribute. The CODE attribute tells the browser where to look for the compiled .class file. It is relative to the location of the source document. Thus if you're browsing http://metalab.unc.edu/javafaq/index.html and that page references an applet with CODE="Animation.class", then the file Animation.class should be at the URL http://metalab.unc.edu/javafaq/animation.class.

For reasons that remain a mystery to HTML authors everywhere if the applet resides somewhere other than the same directory as the page it lives on, you don't just give a URL to its location. Rather you point at the CODEBASE. The CODEBASE attribute is a URL that points at the directory where the .class file is. The CODE attribute is the name of the .class file itself. For instance if on the HTML page of the previous section you had written

<APPLET

then the browser would have tried to find HelloWorldApplet.class in the classes directory in the same directory as the HTML page that included the applet. On the other hand if you had written

then the browser would try to retrieve the applet from http://www.foo.bar.com/classes/HelloWorldApplet.class regardless of where the HTML page was.

In short the applet viewer will try to retrieve the applet from the URL given by the formula (CODEBASE + "/" + code). Once this URL is formed all the usual rules about relative and absolute URLs apply.

You can leave off the .class extension and just use the class name in the CODE attribute. For example,

If the applet is in a non-default package, then the full package qualified name must be used. For example,

In this case the browser will look for http://www.foo.bar.com/classes/com/macfaq/greeting/HelloWorldApplet.class so the directory structure on the server should also mirror the package hierarchy.

The HEIGHT and WIDTH attributes work exactly as they do with IMG, specifying how big a rectangle the browser should set aside for the applet. These numbers are specified in pixels and are required.

Spacing Preferences

The <APPLET> tag has several attributes to define how it is positioned on the page.

The ALIGN attribute defines how the applet's rectangle is placed on the page relative to other elements. Possible values include LEFT, RIGHT, TOP, TEXTTOP, MIDDLE, ABSMIDDLE, BASELINE, BOTTOM andABSBOTTOM. This attribute is optional.

You can specify an HSPACE and a VSPACE in pixels to set the amount of blank space between an applet and the surrounding text. The HSPACE and VSPACE attributes are optional.

The ALIGN, HSPACE, and VSPACE attributes are identical to the attributes of the same name used by the <IMG> tag.

Alternate Text

The <APPLET> has an ALT attribute. An ALT attribute is used by a browser that understands the APPLET tag but for some reason cannot play the applet. For instance, if you've turned off Java in Netscape Navigator 3.0, then the browser should display the ALT text. Note that I said it should, not that it does. The ALT tag is optional.

ALT is not used by browsers that do not understand <APPLET> at all. For that purpose <APPLET> has been defined to require a closing tag, </APPLET>. All raw text between the opening and closing <APPLET>tags is ignored by a Java capable browser. However a non-Java capable browser will ignore the <APPLET> tags instead and read the text between them. For example the following HTML fragment says Hello to people both with and without Java capable browsers.

Naming Applets

You can give an applet a name by using the NAME attribute of the APPLET tag. This allows communication between different applets on the same Web page.

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