Vert.x requires JDK 1.7.0 or later. Make sure that the JDK is installed and on the PATH.
If you are using an OSX, you can install vert.x with brew as follows:
$ brew install vert.x
You can download brew from brew.sh.
If you are not using OSX, then download the distribution and follow the examples here.
Unzip the distribution. Then add the Vert.x bin directory to your PATH.
$ tar -zxf ~/Downloads/vert.x-2.0.0-final.tar.gz
or
$ unzip ~/Downloads/vert.x-2.0.0-final.tar.gz