Import GatewayServer from the py4j package so that the unqualified class can be used in the application

import py4j.GatewayServer;

Minimal working example:

//AdditionApplication.java
import py4j.GatewayServer;

public class AdditionApplication {

  public static void main(String[] args) {
    AdditionApplication app = new AdditionApplication();
    // app is now the gateway.entry_point
    GatewayServer server = new GatewayServer(app);
    server.start();
  }
}

Compile (make sure that the -cp path to the py4j is valid, otherwise adjust it such that it points to the right place):

javac -cp /usr/local/share/py4j/py4j0.9.jar AdditionApplication.java

Run it:

java -cp .:/usr/local/share/py4j/py4j0.9.jar AdditionApplication

Now, if you run your python script, in the terminal where the java AdditionApplication is running you should see something like:

>>> Hello World!