First off. . . there is nothing wrong with installing RPMs in Slackware. Don't spread FUD.
That's why Slack comes with the RPM program, and the rpm2tgz program (converts RPMs into .tgz files for easy installation.)
But what you have is a rpm.bin file. It extracts itself into an RPM file for installation.
What you want to do is download the other linux file provided by sun. . . it looks the same but does not have rpm in it's name.
Then as root just
chmod +x JavaInstallationFile.bin #whatever it is called. . .
It will guide you through the setup and installation. . .