When exporting to android it sais java is not installed.
But i've java on my machine.
what do I need to do
You actually need Java JDK to generate the keystore.
You can download it from here:
Just make sure after you install it that your operating system environment path is pointing to the JDK version and not the JRE version.
To verify (on Windows) open the command line prompt (Start menu > cmd) and type in "Keytool". If it gives you undefined, it means that something is not done right.