Just do the following:
1. Ensure you have java installed, in a terminal execute the following command:
You should get a java version when you have execute the previous command, otherwise you should installed first.
If you install java then you must add the JAVA_HOME/bin to the PATH variable in order to java to be recognized when you execute the installer.
2. Once you have your java in the PATH variable, the execution of the java -version command must returns you the java version you have installed.
Finally just run the following to start the installer (assuming you are using the generica jar installer):
java -jar weblogicinstaller.jar
The installation should start.
Hope this helps you