title: How to call multiple interstitial ad?
body: <p>I added interstitial ad (+banner) to my app that contains one activity, no problem with banner but the interstitial ad shows only at app launch one time, my app don't contain any buttons or actions just a pdfview, what I want to do is showing the ad every 5mins when the user reading the pdf. I searched the similar questions but couldn't get it. here my code to load and show the ad :</p>
  
  <pre><code>    AdView mAdView = (AdView) findViewById(R.id.adView);
      AdRequest adRequest = new AdRequest.Builder().build();
      mAdView.loadAd(adRequest);
  
      // Prepare the Interstitial Ad
      interstitial = new InterstitialAd(PDFViewActivity.this);
      // Insert the Ad Unit ID
      interstitial.setAdUnitId("ca-app-pub-3940256099942544/1033173712");
      interstitial.loadAd(adRequest);
      // Prepare an Interstitial Ad Listener
      interstitial.setAdListener(new AdListener() {
          public void onAdLoaded() {
              // Call displayInterstitial() function
              displayInterstitial();
          }
      });
  }
  
  public void displayInterstitial() {
  // If Ads are loaded, show Interstitial else show nothing.
      if (interstitial.isLoaded()) {
          interstitial.show();
      }
  }
  </code></pre>