title: How to collect list from lambda expression
body: <p>I am writing a method which will return a list of regiondata, i am doing in following manner but getting error</p>
  
  <pre><code>@Override
      public List&lt;RegionData&gt; getAllRegionsForDeliveryCountries()
      {
          final List&lt;RegionData&gt; regionData = new ArrayList&lt;&gt;();
          final List&lt;String&gt; countriesIso = getCountryService().getDeliveryCountriesIso();
          regionData = countriesIso.stream().map(c-&gt;i18nFacade.getRegionsForCountryIso(c)).collect(Collectors.toList());
          return regionData;
      }
  </code></pre>
  
  <p>I am getting error on </p>
  
  <pre><code>type mismatch: cannot convert from List&lt;List&lt;RegionData&gt;&gt; to List&lt;RegionData&gt;
  </code></pre>
  
  <p>on line regionData = countriesIso.stream().map(c->i18nFacade.getRegionsForCountryIso(c)).collect(Collectors.toList());</p>
  
  <p>The function i18nFacade.getRegionsForCountryIso(c) is returning a list of region data, I want to combine these lists into single list.
  I tried with lambda but unable to do so.</p>