How Can i use @String xml in ad unit - admob App Open Ads

Question

Here Sample Of My code

Strings.xml

<string name="AppOpen_id">ca-app-pub-3940256099942544/3419835294</string>

AppOpenManager.java

private static final String AD_UNIT_ID = "ca-app-pub-3940256099942544/3419835294";

For Example I Need To Get App-pub from string something Like @string/AppOpen_id

How can I Do it !

AppOpenManager.java Full Code

/** Prefetches App Open Ads. */
public class AppOpenManager implements LifecycleObserver, Application.ActivityLifecycleCallbacks {
    private static final String LOG_TAG = "AppOpenManager";
    private static final String AD_UNIT_ID = "ca-app-pub-3940256099942544/3419835294";
    private AppOpenAd appOpenAd = null;

    private AppOpenAd.AppOpenAdLoadCallback loadCallback;

    private final MyApplication myApplication;
    private Activity currentActivity;
    private static boolean isShowingAd = false;
    private long loadTime = 0;


    /** Constructor */
    public AppOpenManager(MyApplication myApplication) {
        this.myApplication = myApplication;
        this.myApplication.registerActivityLifecycleCallbacks(this);
        ProcessLifecycleOwner.get().getLifecycle().addObserver(this);
    }


    /** LifecycleObserver methods */
    @OnLifecycleEvent(ON_START)

    public void onStart() {

        showAdIfAvailable();
        Log.d(LOG_TAG, "onStart");
    }


    public void showAdIfAvailable() {
        // Only show ad if there is not already an app open ad currently showing
        // and an ad is available.
        if (!isShowingAd && isAdAvailable()) {
            Log.d(LOG_TAG, "Will show ad.");

            FullScreenContentCallback fullScreenContentCallback =
                    new FullScreenContentCallback() {
                        @Override
                        public void onAdDismissedFullScreenContent() {
                            // Set the reference to null so isAdAvailable() returns false.
                            AppOpenManager.this.appOpenAd = null;
                            isShowingAd = false;
                            fetchAd();
                        }

                        @Override
                        public void onAdFailedToShowFullScreenContent(AdError adError) {}

                        @Override
                        public void onAdShowedFullScreenContent() {
                            isShowingAd = true;
                        }
                    };

            appOpenAd.show(currentActivity, fullScreenContentCallback);

        } else {
            Log.d(LOG_TAG, "Can not show ad.");
            fetchAd();
        }
    }


    /** Request an ad */
    public void fetchAd() {
        // Have unused ad, no need to fetch another.
        if (isAdAvailable()) {
            return;
        }
        loadCallback =
                new AppOpenAd.AppOpenAdLoadCallback() {
                    /**
                     * Called when an app open ad has loaded.
                     *
                     * @param ad the loaded app open ad.
                     */
                    @Override
                    public void onAdLoaded(AppOpenAd ad) {
                        AppOpenManager.this.appOpenAd = ad;
                        AppOpenManager.this.loadTime = (new Date()).getTime();
                    }

                    /**
                     * Called when an app open ad has failed to load.
                     *
                     * @param loadAdError the error.
                     */
                    @Override
                    public void onAdFailedToLoad(LoadAdError loadAdError) {
                        // Handle the error.
                    }

                };
        AdRequest request = getAdRequest();
        AppOpenAd.load(
                myApplication, AD_UNIT_ID, request,
                AppOpenAd.APP_OPEN_AD_ORIENTATION_PORTRAIT, loadCallback);
    }

    /** Creates and returns ad request. */
    private AdRequest getAdRequest() {
        return new AdRequest.Builder().build();
    }


    /** Utility method to check if ad was loaded more than n hours ago. */
    private boolean wasLoadTimeLessThanNHoursAgo(long numHours) {
        long dateDifference = (new Date()).getTime() - this.loadTime;
        long numMilliSecondsPerHour = 3600000;
        return (dateDifference < (numMilliSecondsPerHour * numHours));
    }

    /** Utility method that checks if ad exists and can be shown. */
    public boolean isAdAvailable() {
        return appOpenAd != null && wasLoadTimeLessThanNHoursAgo(4);
    }

    @Override
    public void onActivityCreated(@NonNull Activity activity, @Nullable Bundle bundle) {

    }

    @Override
    public void onActivityStarted(@NonNull Activity activity) {
        currentActivity = activity;
    }

    @Override
    public void onActivityResumed(@NonNull Activity activity) {
        currentActivity = activity;
    }

    @Override
    public void onActivityPaused(@NonNull Activity activity) {

    }

    @Override
    public void onActivityStopped(@NonNull Activity activity) {

    }

    @Override
    public void onActivitySaveInstanceState(@NonNull Activity activity, @NonNull Bundle bundle) {

    }

    @Override
    public void onActivityDestroyed(@NonNull Activity activity) {
        currentActivity = null;
    }
}

Answer 1

lol))) 
public AppOpenManager(MyApplication myApplication) {
        this.myApplication = myApplication;

this.AD_UNIT_ID = myApplication.getString(R.string.AppOpen_id);
        this.myApplication.registerActivityLifecycleCallbacks(this);
        ProcessLifecycleOwner.get().getLifecycle().addObserver(this);
    }