CS 201 - Enabling Applets in your browser
Most browsers have discontinued support for Java applets. Here are
instructions for how you can still run Java applets. One method is to
run them using the Java JDK's appletviewer from the commandline. The
other is to use browsers that still supports applets (Internet Explorer
on PCs, and Firefox v52.9ESR on Macs), and configure them to allow
running applets on our course page.
If you have the Java SDK installed (i.e., you can run "javac" from the
command line), you can also run applets directly from the command line
using the tool "appletviewer". Go to the web page containing the
applet and copy the URL, then run appletviewer with the URL as
command-line argument. For instance, to run the Buggle applet from
lecture 5, type:
Using the browser on a PC
On a PC, Internet Explorer still supports running applets. Start IE
and continue at "Enabling Java" below.
Using the browser on a Mac
If you have an older version of Safari (11 or earlier), you can use
Safari. If you have Safari 12 you'll have to install and use Firefox 52 ESR. See
for instance this post.
Download Firefox 52 ESR from
the official site
or download this local copy.
Install Firefox by dragging the icon to the Applications folder. If you already have
a newer version, select "keep both" and it will likely save this older version
After installing, it is important to (quickly) disable updates within
the Firefox preferences or it will update to a newer version that also
doesn't support Java. Start Firefox, go to Preferences (Apple-comma),
then Advanced, select the Update tab, and click on "Never check for
updates". This is a security risk, so don't use this version of
Firefox for general web browsing, only for our course page.
After starting a browser that supports Java, head to www.java.com and download Java. Note
that this is a different Java than the Java SDK you downloaded earlier
in the semester. When in doubt, click on "Do I have Java?" and follow
Firefox users: Ignore the yellow box and look at the line underneath
("Firefox 52 ESR users"). Click at "click here".
If you see a gray box, click on Activate Java.
Click on Allow and Remember. If it asks you to upgrade Java, go ahead
and upgrade. But do not allow it to "uninstall older versions" of
Java since that might uninstall your Java SDK.
If successful, you should see "Congratulations! You have the recommended
version of Java installed."
Enabling Applets on our course page
The final step is to convince Java that our CS 201 applets are safe
(they are!). The applets on our course page are considered
"untrusted", so we need to add them to an "exception list". To do
this, open the Java Control Panel:
Mac: Open System preferences, and click on Java
PC: From start menu, search for "java". Select "Configure Java".
Once the Java Control Panel is open, click on Security tab.
Finally, for the changes to take effect, you'll have to close and restart your
- Make sure "Enable Java content in the browser" is checked
- Make sure security is "High", not "Very high"
- For the Exception Site List:
To test it, navigate to one of the applets on our course page (e.g.,
"Buggles" from lecture 5). If you get a warning "plug-in blocked",
select "enable the plugin". When prompted "always allow for
cs.middlebury.edu", say "yes".
Hopefully it will work now! If not, please come see me.
For PCs, more information on how to enable Java in various browsers
under Windows can
be found here.