a partial Java application program designed to run inside the womb of a web browser, with help from some
predefined support classes.
java.applet.Applets must run inside a web browser (or AppletViewer).
You can also run them in Java Web Start to avoid the peculiarities of
individual browsers. You cannot run them from the java.exe command line. To spawn a web browser from within an
application to get it to display an Applet, see the tips under HTML rendering. Applets are typically automatically
downloaded over the web freshly every time they are executed. They can also be run from local hard disk. In
contrast, applications cannot be run inside a browser, though it is possible to make a dual mode program
that can run either as an Applet or application. Applets
run on the client’s machine. In contrast, Servlets run on the host webserver.
Applets are harder to write than applications. I would recommend that beginners
start with applications. With Applets you have the following complications:
The big appeal of Applets to the beginner is that you can post your handiwork on the
web for everyone to play with and admire.
- Your entire logic must fit in the straight jacket of four methods init,
start, stop and destroy.
- Unsigned (ordinary) Applets are restricted in hundreds of not-well-documented
ways. They are not even allowed to read files.
- An Applet must run inside a browser. This adds an extra level of complication
and uncertainty as different browsers have different bugs.
- Unless you spin off a separate Thread, an Applet has no mechanism to do any
calculation that takes more than a fraction of a second.
The easiest way to write an Applet is to start with a working one, perhaps
one of mine. Write it as a hybrid, and debug it as an
application. Once you have it working as an application, test it as an Applet in a
browser. If you have an IDE (Integrated Development Environment) like Intellij Idea, you can run it in the IDE as an Applet
as an intermediate phase between testing as an application and as an Applet in a
Unsigned Applet Restrictions
To make Applets very safe to run, even when they were composed by teens with the
morals or skill of Beavis and Butthead, Applets are severely restricted. Unsigned
Applets (without special permission to bypass security) are not permitted to:
- talk to any server but the one you were loaded from. No talking to strangers. If they were loaded from a
local disk, they can’t talk to any webserver at all. They can’t load classes, read files, or
have socket communications with any webserver but mom, the server htey were loaded from. Applets can send/receive email to/from a different host, but only via the home host.
- I have discovered by experiment that when an Applet runs locally, it is only
allowed to read files in the same directory or in a subdirectory of that directory. It can’t read files
in the parents or sibling directories, just child/grandchild directories. Oddly, it does not matter where the
jar itself is, but where the web page is that has the <applet tag. The files
the Applet reads have to be downstream of that page. You will notice
multiple snippet subdirectories all over my website. This is because Applets could not get at a central snippet directory. The place where I
put the code snippets for a given webpage has to be in a branch off the directory containing the web page. My
only other alternative would be to always put the code snippets in the same directory as the web page. I am not
sure if the same restriction applies to Applets run on a webserver.
- I have discovered by experiment that when an Applet runs from a website, it is
only allowed to read files in the same directory as the web page or in a subdirectory of that directory,
(downstream from the webpage). It can’t read files in the parents or sibling
directories, just child/grandchild directories. It does not matter where the jar is, just the web page and the
files that you try to read. This means unsigned Applets usually end up bundling
everything they need to read as resources in the jar.
- I have not experimented with https:. Please let me know if you can use
https in an unsigned Applet and if you can mix http: to fetch the Applet jar and http: to
fetch the data.
- read or write local files on the client machine. They are not even allowed to look in a directory or
test for the existence of a file. You can however read a file (resource) embedded in
the jar with Class. getResource or Class.getResourceAsStream. It can also read from the server via a URL. Even when your Applet is loaded from hard disk, it
still may not do file I/O even via file: URLs (Uniform Resource Locators).
- Use System.setOut
or System. setErr to redirect the console.
- Look at the restricted system properties, or get an enumeration of all the system properties. See Wassup. Don’t use Color.
getColor which interrogates the system properties.
- Monitor mouse motion.
- Print in Java version 1.1, though you can in JDK (Java Development Kit) 1,2+. The user has to ok the
- Send email to a server other than the one it was loaded from.
- Talk to a serial port.
- Talk to a parallel port.
- Change thread priority, even lower it.
- Read or write the clipboard. However, users can manually cut/paste your AWT (Advanced Windowing Toolkit) components without security
clearance. The restriction is on programmatic control of the clipboard. Swing components have no cut/paste
ability at all.
- Install software.
- Execute any native code. If you use native JNI (Java Native Interface) code, things get really complicated vis a vis
security and signed Applets with native code. You are better off to use Java Web
- Exec external programs.
- Issue an RMI (Remote Method Invocation) call to a remote object running on a different server than the Applet’s.
- Determine the structure of an object (fields, methods, values, etc.) using the Reflection API (Application Programming Interface).
- Use the Preferences API to store or look at configuration information in the registry.
- You can use Properties.load
so long as you read the resource with MyClass.class. getResourceAsStream
If your Applet needs to do any of the above things, it must
Now that IE (Internet Explorer) has dropped Java, it is reasonable to ask your clients to upgrade to the latest Java,
understanding that some will not. For them, you must develop or at least test on earlier versions. Don’t
just assume that just because you did not use any new features that you are home free.
Standalone Java applications are not so limited. Exactly what the limitations are is controlled by the
security manager in the browser. If the user installs an alternate security class, the Applet may have more powers. The security restrictions are controlled entirely by the browser.
There is nothing to stop you from writing a non-conforming browser that has quite different security restrictions
for Applets. However, in practice, you write code to sign your jars and bypass each of
the five different security schemes used in browsers.
Programmers bitterly complain about these restrictions. The restrictions protect the end user from malicious
web Applets they might encounter on the web. Without such protection, vicious
Applets could destroy the user’s hard disk, print reams of paper, phone out on a
spare serial port and rack up long distance bills, go sniffing on the LAN (Local Area Network) for the company books… You
don’t want to give those powers to psychotic strangers — those same people who stay up late at night
- When you use a browser to host your Applets, the JVM (Java Virtual Machine) is started once, when you run your first Applet. All
Applets run in the same JVM. They even share the same Thread. You must be careful in your Applet not to hog the
CPU (Central Processing Unit), otherwise you will throttle other Applets. This loading strategy is why the first Applet takes longer to
start. In contrast, when you run applications, each get their own logically distinct JVM, but they share DLLs (Dynamic Link Libraries)
- Don’t try to make Applets work on your website
with naked class files. Always bundle everything, classes, gifs, configuration scripts etc. up into a jar. This
bypasses many classpath headaches, and it downloads faster. Further, the chances are much better your
Applet will work first time on the website once you get it working locally out of a
- Applets are a pain in the behind. If you possibly can, use Java Web Start instead.
- Don’t try to use any of the Applet methods in your constructor such as
getCodeBase. They depend on a private field called appletStub that does not get initialised until just before your init
method is called. You will get NullPointerExceptions if you fail to heed this
- Unsigned Applets are extremely restricted in what they can do. Carefully review
the list above. In particular, Applets
cannot write to the local hard disk or talk to a server other than the one they were loaded from.
will get all the Applets on the page, not just other instances of the current class.
Further, sometimes this instance is included, sometimes it is not. Don’t
count on it working either way.
Normally, all applets run in the same JVM instance.
This allows instances of an Applet on a page to share information via static variables and calling each other’s
As of JRE1.6.0_10 you can no longer count on this. The plug-in may run Applets in separate JVMs (Java Virtual Machines).
Applets in different JVMs will not be visible to each other when
calling AppletContext.getApplets() even if they are within the same document,
which would seem to contradict the Java API:
Oracle’s Javadoc on getApplets
class : available:
Apparently it is possible to encourage the plug-in to start applets in the same VM if the <applet> tag has a
'java_arguments' param with an identical set of arguments, regardless of what these options actually specify. However, it is explicitly not guaranteed that this will work. Also, according to Oracle
There is no way to name a JVM instance used to launch a particular applet and forcesubsequent applets into that JVM
Windows and Variable Resolution
Windows has a feature whereby the user can increase the size of the default system font. Let’s say you increase it to 125%.
Now, when you use an Applet in Internet Explorer, IE will give you Applet region to paint
25% bigger than you asked for on your
<applet tag. Windows/IE is
inviting you as an Applet programmer to use a 25% bigger font inside your Applet and to magnify your images
by 25% to make them easier for the user to see. If you ignore the extra space, your Applet will appear with small
fonts, small icons, and a big wide empty border.
HTML (Hypertext Markup Language) to Invoke an Applet
That stray-looking > after mayscript is not a mistake. It has to be there to close the opening
<applet tag. This way the Applet has lots of room to
display. If you leave them, out your Applet may be rendered off the right edge of the
screen, where you probably won’t see it.
You may not leave out the code=com.mydomain.myproject.MyClass.class even if you have specified the Main-Class
in the manifest. I have no idea why.
I repeat. Always bundle your Applet
and resources into a jar!
- You can then invoke your Applet from any page.
- The classes download faster.
- It is clear exactly which classes your Applet may use and not use.
- There are no classpath mysteries.
- It is always clear which version of the class files you are using.
- Everything just works more smoothly.
Here is tip to find the optimal size parameters. Run the Applet as an application.
Drag the frame to the optimum size. Use Paint Shop Pro to capture a screen
snapshot of the frame, excluding the menu bar. Then look in the lower right corner of the PSP window
(or use Mioplanet
discover the size for the <applet height and width
tags. Then measure including the menu bar to discover the size for the Frame.
setSize( width, height ) when running as an application. It will need about 24 pixels
extra height. This trick saves a lot of guesswork and experimentation to home in on the optimal values.
When debugging Applets, remember to click Shift-Reload
in your browser, not just plain Reload to attempt re-running with your new version.
Shift-Reload supposedly flushes the cache of class files. This usually does not work. You have to exit the
browser and restart. It is a good idea to put something unique in every incarnation of your code so you can tell
if you are running the old or new code. I do it by flipping a background colour or setting a micro version
You can go crazy debugging Applets because the browser sometimes caches old copies
of jars, classes, html… It is best to start each test with at least a fresh loading of your browser,
preferably with all its caches deleted using a bat file before each test. I often start different a different
browser for each test to get a clean start, e.g. Opera, Firefox, SeaMonkey, Netscape, IE.
It is best to debug as an application, then at the last minute convert to an Applet.
Applets are invoked to run in browsers by the <applet…> tag.
Applets won’t work if you load them directly with your browser as if they
were web pages! The HTML commands for firing up an Applet are exceedingly picky.
It matters whether you have .class or not. I suggest you look at the files that come
with the Conversion Amanuensis to see how to run an Applet/Application with/without
jars, locally, on a website, with various browsers and run times. Here is the basic structure:
||The name of the class file for the Applet. You are not allowed to specify an
absolute URL (Uniform Resource Locator) or absolute fully qualified hard disk filename. Strange as it sounds, Sun originally said you
must specify the trailing .class, but now they suggest you leave it out. Some
some browsers let you do it either way. The new Sun tutorials shows it without the .class. If you do it the way different from the way the browser likes, you will just get a
gray square with no error message, even if you have manifest Main-Class
entry. All the recommended browsers will handle it
||width of entire Applet display in pixels. There is nothing the Applet can do itself to change this. If you needed variable size you would have to resort to
specified as a percentage e.g. width=100% or with CSS (Cascading Style Sheets) commands. Then
the Applet will grow and shrink with the enclosing window.|
||height of entire Applet display in pixels. There is nothing the Applet can do itself to change this.|
||Resource file, classes etc. Your ARCHIVE parameter must have a list of the
absolute or relative jar files, separated by commas (no spaces). (Watch out! The ARCHIVE tag in <OBJECT is space-separated!) If you have too
little or too much qualification, or if you fail to use the file naming conventions of your server, you
will be in trouble. You are probably best to use absolute URLs
or fully qualified hard disk file names.
Whether the archive is supposed to be relative to the current HTML directory, the CODEBASE, or all elements of the classpath is unclear. The forms of archive I use most are
archive=myapp.jar archive=../myapp.jar and archive=somedir/myapp.jar.|
||I suspect CODEBASE is simply broken in the current implementations. Theoretically it is the absolute or
relative URL/directory where class files are, like a one-element classpath. Normally the class files are in
the same directory as the html, so you don’t need it. In practice, I have found your CODEBASE
parameter must have an absolute http:// -style reference to the base directory
where the code is stored. The codebase is only needed when your code resides somewhere other than where the
html page was loaded from. For a local hard disk, the only thing I could get to work on NT with all
browsers and Appletviewers is leaving the CODEBASE out entirely which causes the CODEBASE to default to the
same directory as where the enclosing HTML page was loaded from. You may find for your platform you have to
code it something like this: file://localhost/C|//MyDir/ or C:\MyDir\. I also further suspect that some browsers will take the a relative CODEBASE as
relative to each element of the CLASSPATH, not relative to the current HTML directory. If the user of the
signed Applet is behind a firewall, for some strange reason, if he invokes the
Applet using the IP (Internet Protocol) rather than the DNS (Domain Name Service) name of the website in the codebase e.g
of CODEBASE=mindprod.com, all works.
Otherwise you get a trustProxy Property error message.|
||pixel width of border above and below the Applet|
||pixel width of border left and right of the Applet|
||how this Applet aligns, treated like an image|
|alt=You need Java to run this Applet
||what to display if no Java interpreter available. Normally this would be the same text that appears
just before the </applet> tag. This optional attribute specifies any
text that should be displayed if the browser understands the APPLET tag but can’t run Java
||Name for this Applet so that other Applets can
communicate with it. Other Applets would do an Applet
Applet.getAppletContext(). getApplet( receiver ) to get a handle on this Applet. You
don’t need this parameter if you use Applet Enumeration Applet. getAppletContext(). getApplets() which gets you a list of all the Applets
running on the page (including yourself).|
||Lets Applet read/write cookies and peek at the page it is embedded in using
||All that stuff above has to be inside the <applet… >, but the
params may not be.|
|<param name=favouriteColour value=orange
||The param statements are Java’s ode to verbosity. They pass
information to the Applet. There can be as many param statements as you like.
Beware of params with decimal points. <param name=cost value=10.00 > When
your Applet runs in Europe, it may be expecting a comma instead unless you
take special precautions.
Param values cannot contain embedded " or newline characters. You can
encode the parameters using HTML entities such as ", > or &#nn;. The browser should automatically
convert them for you to the equivalent character when you do your getParam.
If the browser does not convert them for you, you can convert the entities back to characters with my
free entities package. I tested recent versions
of Opera, Netscape, Firefox, Mozilla and IE and they call converted entities to characters automatically.
Unfortunately, there is no & entity for \n. and
do not work. You will have to roll
your own convention, perhaps using the character pair \n or some rarely used
character such as ~ or ` to stand in for newline. You
can’t use <br> because < and
> are awkward characters in their own right.
Awkward characters are defined as ones that have be specially
escaped/quoted/represented to use them literally because they have special meaning as
commands/delimiters. This encoding is natural. Fussing with entities only kicks in when you have awkward
characters. Further, the way you encode parameters is completely familiar — almost the same way you
encode awkward characters in HTML body text. Watch out for &#xnnnn; and
&#nnnn; style entities. What they mean depends on the enclosing HTML
Alternatively, you could write a little utility to use java.net.
URLEncoder to encode the string, then manually include it as the param value,
then use java.net. URLDecoder inside the
Applet to make sense of the parameter. URLEncoder
encodes space as + and special characters as %xx hex,
so you can do the encoding in your head once you see a few examples. The catch is, once you hook up
URLDecoder to a param, you can’t use that param anymore for plain text,
at least not completely transparently.
If you wanted to disguise the value, you could encode it with base64 or base64u armouring.
Applet parameter names are case insensitive (Case does not matter. Names can be upper or
lower case). Applet parameter values are case sensitive (passed exactly as written to your
Applet’s getParameter. If you want lower case, use parmValue.) toLowerCase().
||image to display if no Java interpreter available.|
|You need Java to run this Applet
||Text that will display on a really stupid browser that has no idea what an Applet tag is.|
||and finally the ending tag for the|
<applet code="MyApplet.class" width="330" height="240">
Make sure you get your <s s ‘s ’s s and >s in the
A more typical Applet invocation might look like this:
alt="Java needed to display this Applet.">
<param name="flavour" value="strawberry">
Java needed to display this Applet.
To run Applets in Internet Explorer 5.5 or Netscape 4.79 with the old
Java version 1.3
Plugin before the courts smacked Microsoft for their violation of their agreement with Sun, you need a hideously
complicated syntax using nested <OBJECT> and <EMBED> tags. The best way to generate them is to use the HTML converter program on your
simple <applet tags. You don’t need them to run with the Plug-in 1.4 in the
recent versions of Opera, Mozilla, Firefox, Netscape and IE. Further, the latest Mozilla can’t even
understand them. Their only advantage is they can arrange to install a Java JRE (Java Runtime Environment) if one is not installed already.
I boycott them on the grounds of terminal ugliness.
<applet, from a CSS point of view, is just another tag. In your CSS style
sheet, you can apply properties to it, adjust the margin spacing, put borders around it… In your HTML
markup you can give it a class or id. Unfortunately Mozilla, Netscape and Firefox all have a common bug and
don’t display a border around Applets even when you ask them to. Opera and IE
<OBJECT> and <EMBED>
In theory, <applet has been deprecated and you should use the more generic,
verbose, error-prone <OBJECT tag. <OBJECT has
some minor nice features, like a standby message and a way of providing alternate implementations if the
user’s browser does not support Java. It can work with serialised Applets. It
works for languages and plug-ins other than Java. However, <OBJECT is still not
as widely supported as <applet, so it is probably wiser to stick with
<applet. See the HTML spec for details.
Starting with JDK 1.4.2, you can arranged that jars be cached at the client site
using the EMBED tag cache_archive parameter.
That was the polite version, but here is what I really think of <OBJECT>
and <OBJECT> tags. Anti-Java, rather corrupt people launched a successful
attempt to derail Java by somehow convincing some weak minded folk at the W3C to deprecate the <applet tags. Browser makers have all
sensibly resisted this foul play and all continue to support <applet. The
replacement is an utterly preposterous and verbose scheme using <OBJECT> and
<OBJECT> tags that works in different ways in different browsers. The scheme
is beyond ridiculous. It is so baroque, you can’t even hand code it. You have to use an automated tool to
convert <applet tags into pages and pages of gobbledegook. Don’t use them!
Tell the W3C (World Wide Web Consortium) and Microsoft to shove their <OBJECT> and <EMBED> and lunatic classids to a foul-smelling place.
Please, do not use these tags!
You can use a simple Jump to Java Button to handle a missing JRE.
Applet ⇒ application: Hybrid Switch Hitters
By adding the following method to your Applet, you can allow it be run either as an
Applet or as an application. I call these dual mode programs hybrids or switch hitters. If your Applet were
called MyApplet, here is the code to add to the MyApplet class to make it also into an application:
Your Applet can get hold of the parameters in the HTML.
That code is quite crude. It will not do such things as:
The easiest way to deal with these problems is to use two Applet constructors, one the
usual default constructor and one that passes the param information in. Inside you can keep track of which mode
you are running in with a boolean you set in the constructor. getParameter( favouriteColour ) will return the String
orange. When you write an Applet often you
will override some of the following methods: init(), start(), stop(), destroy() and
- Simulate the getParameter method to get at the Applet parameters.
- Adjust the coordinate system so part of the Applet is not hidden under the
Frame menu bar. Layout managers deal with this automatically, but if you do absolute
positioning, you have to compensate manually..
- It does not simulate getAppletContext. Code defensively to deal with a
There is equivalent code for JApplet.
Switch Hitter: application ⇒ Applet
What if you already have an application? how to you allow it to run also as an Applet?
An Applet is just a Panel with init, start, stop and destroy methods. Write an Applet shell that does a this.add to add your application into the Applet in its init method, just as you would any other Panel.
Though it is possible to create transparent and translucent components using colours with the alpha channel ( the
fourth number in new Color (
red, green, blue, alpha )) set to something other than 0xff, I have found no way to
make the Applet or JApplet itself transparent. You could
pass the colour of the web page’s background in as an Applet param or have
were using a plain untextured background.
Loading A Web Page
Often you want to display some other web page. You can trick the browser into doing that for you with:
this.getAppletContext().showDocument( url, window );
Your Applet does not get to see the web page. It goes straight to the browser for
rendering. Because this feature can be so easily abused to wallpaper the user’s screen with popups, it is
now often blocked.
Communication between Applets running on the same page, it turns out, is much simpler
than you might imagine. First, there is only one program per web page running. In fact there is only one
program per browser running. Applets are just a bunch of ordinary objects.
Applets from the same class share the same static variables! Objects can call each
other’s methods. They are all in the same address space. There is thus almost zero problem with interApplet
communications. Your only problem is finding the other Applet objects on your page to
talk to. There are two mechanisms for that,
An Applet propagates information around by putting it in static variables, or by
passing parameters to the methods of other objects to get them to do something with the information. There is
only one thread, not one per Applet. You can’t just deposit information and
expect the other Applets to notice the change.
- Applet Applet. getAppletContext(). getApplet( receiver )
that accesses another Applet uniquely identified via a name you assign in the HTML
<applet name= tag.
- Applet Enumeration
that gets you a list of all the Applets, of any class, not just yours, running on
the page (including yourself).
The browser may decide to kill (forget) Applets not on the current page, and then
again it may not. Presumably, if you held onto a reference to offscreen Applets in
your onscreen Applet, or in a common doubly linked object, those offscreen objects
would have to stay alive.
Applets use the ordinary local classpath. This can cause trouble since the
developer’s classpath and the end user’s classpath won’t usually match. There are two sorts of
trouble that ensue:
On the other paw, the Applet classpath can work in the developer’s favour. If an
Applet requires a huge support class library, he can ask the user to download and
install it on his local hard disk and point the classpath to it (or put it in the ext directory). Then the class
library will be immediately available every time the Applet runs.
- If you have any classes not in a package, these non-uniquely named classes could conflict with ones on the
end-user’s local hard disk. To avoid this problem, put any classes ever used by Applets in some globally uniquely named package, e.g.
- You, as developer, may forget to include a necessary class in your jar, usually from some peripheral
package. It will work fine on your machine, but will fail on the customer’s machine. On your machine, the
JVM finds the missing class via the classpath. On the end user’s machine that search fails.
- You as developer may test an Applet jar, yet actually may be using some fresher
classes on your local hard disk. You inadvertently ship stale code.
Applet vs Application
When you are starting a project, which should it be, an Applet or application or both?
The advantages of using an Applet are:
The disadvantages of using an Applet are:
- You can get the browser to render HTML for you.
- You can direct the browser to fetch and display material off the web.
- People run your Applet code as a side effect of viewing a web page. They are
much more willing to do that than download and install your code.
- The user automatically gets the latest version of the software.
- There is nothing to install.
There is a third possibility that has some of the advantage of both Applet and
application called Java Web Start.
- To do anything interesting, you must use signed Applets. There are many
different signing schemes to support. Signing is complicated.
- Applets must co-exist with a browser. There is less RAM (Random Access Memory) available to work.
- Applets must co-exist with a variety of browsers and their variety of bugs and
lack of support. IE supports only Java 1.14 with no RMI, Swing, Collections etc. It is almost impossible to
write code that dodges all the bugs in all the browsers.
- Applets must be loaded over the Internet afresh each time. This can be time
consuming for fat ones. Modern browsers now cache Applets, so this is no longer a
- Web Start is designed to distribute and update applications, not Applets.
- To start an Applet, you must first start a browser.
- You can’t use native code compilers on Applets, only applications. This
means your speed will be limited to the JVM supported by the browser.
- You may not be able to force the user to update the browser to something recent.
Applet vs Servlet
The current fashion is to use Servlets exclusively for all web based applications. I
think this is idiotic. It has made data entry even more primitive than it was on the keypunch. The advantages of
using Applets over Servlets are:
The disadvantages of using Applets over Servlets are:
- With Applets, the user can find out about keying errors right away, not with
cryptic messages that appear only after you hit submit and wait several
- With Applets, data entry can be much more sophisticated, with keystroke
validation, code lookup, pattern validation, bounds checking, mandatory field validation, prompting, help
- With Applets, data communications can go on in the background and can be cached
or procrastinated giving the illusion of instant response.
- With Applets, you don’t have to fill in a giant form only to discover the
server won’t accept it.
- With Applets, you can run your applications on a cheap vanilla HTML server. You
don’t need a complex, expensive to maintain, Servlet womb.
- With Applets, you don’t have to resort to dog’s breakfast kludges
like Ajax to provide even tiny bits of client side intelligence.
- With Applets, you have have sufficient local intelligence to send much terser
binary compressed messages back and forth with the server. You can also exchange serialised Object trees.
- With Applets, a recent Java must be properly installed at the client. This is
more difficult to arrange than you might imagine especially with the FUD (Fear Uncertainty and Doubt) from Sun’s competitors spreading
misinformation about the danger of using Java when actually it is the safest language going.
- With Applets, you can’t use low cost web designers to help create your
applications. With Servlets and a framework markup language the designers
don’t have to write Java code, just HTML, peppered with a bit of gibberish.
- With Applets that connect with a database, you need a mixture of client size and
server side code. This requires two sets of skills, and keeping server and client size code in sync.
- Applets that do almost anything interesting have to be digitally signed. This is
an annoyance to users and frightens them off.
Applet vs WebStart
The advantage of using an Applet over Java Webstart are:
The advantages of using Java Webstart over Applets are:
- Once Java is loaded it will render immediately. It will render inline on your webpage. I use Applets to
display prices on this website in the user’s local currency. There my be dozens of tiny applets on a
single page. Java Web Start apps take an inordinately long time to launch. One reason is they always launch a
private copy of java.exe for each app.
- Applets just run. You don’t need to persuade the user to click something, or give permission. They
are embedded in ordinary HTML pages.
- The app does not run inside the browser. The browser cannot interfere. If you test with one browser, your
app will work with them all. Applets can be a pain, working in one browser but not
- The app does not get downloaded each time, only when it has changed.
- The user can run your app even when disconnected from the Internet.
In Java version 1.5 or later there is a splash logo that comes up as your Applet loads. It sort of a radiant
Sun-like image. You can modify that with a magic <param tag that provides an
alternate scalable image.
Applets can play *.au files, (and
You can control the browser’s JVM runtime parameters (see java.exe) that control stack and heap sizes etc. from the Java Control Panel. click Start ⇒ Control Panel ⇒ Java ⇒ Java ⇒ Java Applet Settings ⇒
View. Add the required parameters in the 4th column, next to the JVM. It does not look like it is
editable, but it is.
Oracle’s Javadoc on Applet
class : available:
Oracle’s Technote Guide on Applet Deployment
Oracle’s Technote Guide on Applet Caching
: avoids <applet
Oracle’s Technote Guide on How to debug Applets running in the plug-in
Oracle’s Technote Guide on Monitoring Applet loads