I've been reading an old Java book where it gives an example on how to sign an applet using javakey. I'm using the openjdk-8 for my development and the command line in Linux and it says command not found: javakey. I know Java has already been acquired by Oracle corporation though I still want to know what happened to javakey, but couldn't find any information on the internet.
It seems you're referring to a combination of the keytool & jarsigner.
But ignore anything in the keytool documentation about generating your own 'self signed' code signing certificate. Self signed certificates are no longer accepted by the Java plug in.