Backend.java

public class Backend<T> {
    private int code;
    private List<T> data;
    private String msg;

    public int getCode() {
        return code;
    }

    public void setCode(int code) {
        this.code = code;
    }

    public List<T> getData() {
        return data;
    }

    public void setData(List<T> data) {
        this.data = data;
    }

    public String getMsg() {
        return msg;
    }

    public void setMsg(String msg) {
        this.msg = msg;
    }
} 

HttpClient.java

public class HttpClient {
    private static HttpService httpService = new Retrofit.Builder()
            .baseUrl("http://192.168.1.24:8088/api/")
            .addConverterFactory(GsonConverterFactory.create())
            .build()
            .create(HttpService.class);
  
    public static List<Company> getCompanies() {
        try {
            return httpService.getCompanies().execute().body().getData();
        } catch (IOException e) {
            e.printStackTrace();
            return null;
        }
    }
   
    public static List<Schedule> getSchedules() {
        try {
            return httpService.getSchedules().execute().body().getData();
        } catch (IOException e) {
            e.printStackTrace();
            return null;
        }
    }
}

HttpService.java

public interface HttpService {
    @GET("companies")
    Call<Backend<Company>> getCompanies();

    @GET("schedules")
    Call<Backend<Schedule>> getSchedules();
}