Singleton class for RetroFit RestAdapter (Retrofit 1.9.0)

ApiManager.java

import retrofit.RestAdapter;

/**
 * Singleton class for Retrofit RestAdapter and API (Retrofit 1.9.0)
 */
public class ApiManager {

    // interface containing HTTP methods as given by Retrofit
    private static RegionApi regionApi;
    // static adapter to be used in entire app
    static volatile RestAdapter restAdapter = null;
    //dynamic endpoints if needed to change base url
    private static DynamicEndPoint dynamicEndPoint;

    private ApiManager() {
    }

    // singleton for RestAdapter
    public static RestAdapter getAdapter() {
        if (restAdapter == null) {
            synchronized (ApiManager.class) {
                if (restAdapter == null) {
                    dynamicEndPoint = new DynamicEndPoint("http://somebase url");
                    restAdapter = new RestAdapter.Builder().setEndpoint(dynamicEndPoint).setLogLevel(RestAdapter.LogLevel.FULL)
                            .build();
                }
            }
        }
        return restAdapter;
    }

    /**Method to get url used by DynamicEndPoint*/
    public static String getBaseUrl() {
        getAdapter();
        return dynamicEndPoint.getUrl();
    }
    /**Method to set Base url for our endpoint*/
    public static void setBaseUrl(String url) {
        getAdapter();
        synchronized (ApiManager.class) {
            dynamicEndPoint.changeEndPoint(url);
        }
    }

    /**Initializing Singleton for RegionApi*/
    public static void initRegionApi() {
        if (regionApi == null) {
            synchronized (ApiManager.class) {
                if (regionApi == null) {
                    regionApi = getAdapter().create(RegionApi.class);
                }
            }
        }
    }
    /**Method to get RegionApi*/
    public static RegionApi getRegionApi() {
        initRegionApi();
        return regionApi;
    }
    /**Method to get RegionApi with changed base url*/
    public static RegionApi getRegionApi(String baseUrl) {
        initRegionApi();
        setBaseUrl(baseUrl);
        return regionApi;
    }
}

DynamicEndPoint

public class DynamicEndPoint implements Endpoint {
    //http://stackoverflow.com/a/27816635/739306
    //http://stackoverflow.com/a/23279628/739306
    //Retrofit 1.9.0

    String baseUrl;

    public DynamicEndPoint(String baseUrl) {
        this.baseUrl = baseUrl;
    }

    public void changeEndPoint(String baseUrl) {
        this.baseUrl = baseUrl;
    }

    @Override
    public String getUrl() {
        return baseUrl;
    }

    @Override
    public String getName() {
        return "default";
    }
}

RegionApi

import retrofit.Callback;
import retrofit.http.GET;
import retrofit.http.Path;
import retrofit.http.Query;

/**
 * Retrofit 1.9.0
 * Simple interface for HTTP methods exposed by Retrofit
 */
public interface RegionApi {

    @GET("/regions")
    public void fetchRegions(Callback<RegionList> callback);
}    

Hi there!
Thank you for the nice example. It's fine for me :)
I have just a question :
Could you explain why you need volatile with the restAdapter property? Is it only because of the DynamicEndpoint which can be change across threads? May I omit it if do not use a dynamic endpoint ?
Thanks for your explanation
DDP