ctk-applet

Run archived Cut-the-Knot Java applets locally from their original web pages.

Give ctk-applet a Cut-the-Knot page URL, and it will find the applets on that page, prepare a local launcher file, and open the selected applet with Java's appletviewer.

Contents

• What this is for
• What most users need
• Requirements
• Install Java 8
• Install ctk-applet
• Quick start
• How selection works
• Commands
• What each command does
• FAQ
• Acknowledgements

What this is for

This tool is for old Java applets from the Cut-the-Knot archive.

Because these applets use the old Java applet system, you need a Java 8 JDK with appletviewer. A newer JDK is not enough.

What most users need

1. Install Java 8 JDK

2. Make sure appletviewer works from a terminal

3. Download ctk-applet

4. Run:

   ctk-applet setup ctk-applet run https://www.cut-the-knot.org/ctk/May2001.shtml --name SilverDollar

Requirements

• Java 8 JDK
• appletviewer available in PATH

Install Java 8

Install a Java 8 JDK that still includes appletviewer.

Linux

Use your distribution packages when available.

Ubuntu/Debian:

sudo apt install openjdk-8-jdk

Arch Linux:

sudo pacman -S jdk8-openjdk

Fedora:

sudo dnf install java-1.8.0-openjdk-devel

openSUSE:

sudo zypper install java-1_8_0-openjdk-devel

You can also use SDKMAN instead of system packages:

curl -s "https://get.sdkman.io" | bash
source "$HOME/.sdkman/bin/sdkman-init.sh"
sdk list java
sdk install java 8.0.482-tem

macOS

With Homebrew:

brew install --cask temurin@8

Or with SDKMAN:

curl -s "https://get.sdkman.io" | bash
source "$HOME/.sdkman/bin/sdkman-init.sh"
sdk install java 8-tem

Windows

Install a Java 8 JDK such as Eclipse Temurin 8, then make sure appletviewer is available in PATH.

Install ctk-applet

Download the binary for your platform from the Releases page.

If you already have Rust installed, you can also run the script directly.

Quick start

Prepare the local Java class archive once:

ctk-applet setup

List the applets found on a page:

ctk-applet list https://www.cut-the-knot.org/ctk/May2001.shtml

Show details for one applet:

ctk-applet show https://www.cut-the-knot.org/ctk/May2001.shtml --index 1

Run one applet directly from the page URL:

ctk-applet run https://www.cut-the-knot.org/ctk/May2001.shtml --name SilverDollar

Save launcher files for later use:

ctk-applet save https://www.cut-the-knot.org/ctk/May2001.shtml --all

Run a previously saved launcher:

ctk-applet run-file saved/may2001/02-SilverDollar.html

How selection works

If a page contains exactly one applet, show, save, and run can be used without --index or --name.

If a page contains several applets, choose one explicitly with either:

• --index N
• --name CODE

Commands

ctk-applet setup
ctk-applet list <url>
ctk-applet show <url> [--index N | --name CODE]
ctk-applet save <url> [--all | --index N | --name CODE] [--out-dir PATH]
ctk-applet run <url> [--index N | --name CODE]
ctk-applet run-file <path>

What each command does

• setup downloads classes.zip when needed and extracts the local classes/ directory
• list shows the applets found on a page
• show prints the applet information for one selected applet
• save writes launcher HTML files to saved/<page-slug>/
• run creates a temporary launcher file and opens it with appletviewer
• run-file opens a previously saved launcher file

FAQ

Is this an official Cut-the-Knot tool?

No. ctk-applet is an independent utility and is not affiliated with or endorsed by Cut-the-Knot.

I came to Cut-the-Knot while looking into take-away game variations and found a remarkable collection of games, applets, and mathematical writing. But the archived applets were no longer easy to run, and it was clear from user discussions that many people did not know how to make them work locally.

This tool was made to help bridge that gap: a small, reliable, and easy-to-use way to run those applets again from their original page URLs.

Why do I need Java 8?

These applets use the old Java applet system and need appletviewer, which is part of a Java 8 JDK. A newer JDK is not enough here.

Why do I need to run ctk-applet setup?

setup prepares the local classes/ directory used by many archived applets.

appletviewer is not found. What should I check?

Make sure you installed a Java 8 JDK, not just a JRE or a newer JDK, and that appletviewer is available in PATH.

Does this download the applet class files from Cut-the-Knot?

It uses the published Cut-the-Knot Java class archive, which mirrors the site's historical classes/ directory. For background, see Help with Java.

Will saved launcher files keep working?

Yes, as long as the local classes/ directory stays in place relative to them.

Acknowledgements

With appreciation for Cut-the-Knot and for the work of Alexander Bogomolny, whose writing and interactive applets made mathematics unusually vivid and approachable.