Environment Setup

Before you can compile and actually run any applet in this track, you need one specific tool that modern JDK installations no longer ship with: appletviewer. This lesson walks through why that matters, what to install, and how to compile and run an applet from the command line.

Installing JDK 8 Alongside a Modern JDK

You do not need to uninstall or replace whatever JDK you already use. The cleanest approach is to install JDK 8 into its own separate folder and point your terminal at it only when you're working through this track, using its full path or by temporarily changing your PATH/ JAVA_HOME in that terminal session.

1. Download a JDK 8 build. Oracle's own JDK 8 requires an Oracle account for newer updates, so most learners use a free OpenJDK 8 distribution instead - Eclipse Temurin (Adoptium), Amazon Corretto 8, or Azul Zulu 8 all work identically for this track.
2. Install it to a dedicated folder rather than letting it overwrite your default JDK - for example C:\Java\jdk8 on Windows or /opt/jdk8 on Linux/macOS.
3. Verify the install by calling java and javac with their full path, for example C:\Java\jdk8\bin\java -version, and confirm it reports a 1.8.0_xxx version string.
4. Optionally, set a JAVA8_HOME environment variable pointing at the JDK 8 folder, so you can reference %JAVA8_HOME%\bin\javac (Windows) or $JAVA8_HOME/bin/javac (macOS/Linux) without retyping the full path every time.

Compiling an Applet

Compilation itself is nothing special - it's the same javac command you already know, just invoked with your JDK 8 compiler. Given a source file named PaintApplet.java:

# from the folder containing PaintApplet.java
javac PaintApplet.java

This produces a PaintApplet.class file in the same folder, exactly as it would for any other Java class. Applets are not compiled any differently from standalone applications - the difference only shows up in how the resulting class is run.

Running an Applet with appletviewer

Since no browser can load an applet, appletviewer exists as a lightweight standalone tool that reads an HTML file, finds an <applet> tag inside it, and opens a small window that behaves like a browser's applet viewport - without needing an actual browser or plugin. You'll meet the full <applet> tag syntax in Embedding in HTML; for now, here's the minimal HTML file appletviewer needs:

<html>
  <body>
    <applet code="PaintApplet.class" width="400" height="300"></applet>
  </body>
</html>

Save that as index.html in the same folder as PaintApplet.class, then run:

# from the folder containing both files
appletviewer index.html

A small window opens hosting your applet, and appletviewer drives its lifecycle (init, start, paint, and so on) exactly the way an old browser plugin would have.

What About My IDE?

Modern versions of IntelliJ IDEA and Eclipse have progressively dropped built-in "Run as Applet" configurations as the API faded out of relevance, and some no longer offer one at all. Rather than fighting an IDE's plugin ecosystem to resurrect applet support, the most reliable and least frustrating way to follow this track is the plain command line with JDK 8's javac and appletviewer, as shown above. You can still write and edit the .java files in whatever editor or IDE you like - you're only bypassing the IDE for the compile-and-run step.