Implement a JAVA class 'Car' with the following properties. A car has a certain fuel efficiency (measured in miles/gallon) and a certain amount of fuel in the gas tank. The efficiency is specified in the constructor, and the initial fuel level is 0. Supply a method 'drive' that simulates driving the car for a certain distance, reducing the fuel level in the gas tank, and methods 'getGas', to return the current fuel level, and 'addGas' to tank up.