genre.json

{
  "genres": [
    {
      "id": 28,
      "name": "Action"
    },
    {
      "id": 12,
      "name": "Adventure"
    },
    {
      "id": 16,
      "name": "Animation"
    },
    {
      "id": 35,
      "name": "Comedy"
    },
    {
      "id": 80,
      "name": "Crime"
    },
    {
      "id": 99,
      "name": "Documentary"
    },
    {
      "id": 18,
      "name": "Drama"
    },
    {
      "id": 10751,
      "name": "Family"
    },
    {
      "id": 14,
      "name": "Fantasy"
    },
    {
      "id": 36,
      "name": "History"
    },
    {
      "id": 27,
      "name": "Horror"
    },
    {
      "id": 10402,
      "name": "Music"
    },
    {
      "id": 9648,
      "name": "Mystery"
    },
    {
      "id": 10749,
      "name": "Romance"
    },
    {
      "id": 878,
      "name": "Science Fiction"
    },
    {
      "id": 10770,
      "name": "TV Movie"
    },
    {
      "id": 53,
      "name": "Thriller"
    },
    {
      "id": 10752,
      "name": "War"
    },
    {
      "id": 37,
      "name": "Western"
    }
  ]
}

Networking.java

import retrofit2.Call;
import retrofit2.Callback;
import retrofit2.Response;
import retrofit2.Retrofit;
import retrofit2.converter.gson.GsonConverterFactory;
import retrofit2.http.GET;
import retrofit2.http.Query;

import java.util.List;

public class Networking implements Callback<Networking.GenreResponse> {
    private static String BASE_URL = "https://api.themoviedb.org/3/";
    private static String API_KEY = "3661f054fd66a3f8a97df3940ff9e3b0";
    private static String LANGUAGE = "en-US";

    public static void main(String[] args) {
        Networking networking = new Networking();

        Retrofit retrofit = new Retrofit.Builder()
                .baseUrl(BASE_URL)
                .addConverterFactory(GsonConverterFactory.create())
                .build();

        TMDBService service = retrofit.create(TMDBService.class);
        Call<GenreResponse> genreCall = service.listGenre(API_KEY, LANGUAGE);
        genreCall.enqueue(networking);
    }

    @Override
    public void onResponse(Call<Networking.GenreResponse> call, Response<Networking.GenreResponse> response) {
        if(response.isSuccessful()) {
            GenreResponse genreResponse = response.body();
            genreResponse.genres.forEach(genre -> System.out.println(genre.getName()));
        } else {
            System.out.println(response.errorBody());
        }

        System.exit(0);
    }

    @Override
    public void onFailure(Call<GenreResponse> call, Throwable t) {
        t.printStackTrace();
        System.exit(0);
    }

    public interface TMDBService{
        @GET("genre/movie/list")
        Call<GenreResponse> listGenre(@Query("api_key") String api, @Query("language") String lang);
    }

    public class GenreResponse{
        List<Genre> genres;
    }

    public class Genre{
        int id;
        String name;

        public int getId() {
            return id;
        }

        public void setId(int id) {
            this.id = id;
        }

        public String getName() {
            return name;
        }

        public void setName(String name) {
            this.name = name;
        }
    }
}