title: How to get the item ID in vaadin
body: <p>Good day everyone! I have a HierarchicalContainer below: </p>
  
  <pre><code>contFinalGrade= new HierarchicalContainer();
          contFinalGrade.addContainerProperty("index", Integer.class, 0);
          contFinalGrade.addContainerProperty("subCode", String.class, "");
          contFinalGrade.addContainerProperty("courseId", String.class, "");
          contFinalGrade.addContainerProperty("parentCourseId", String.class, "");
          contFinalGrade.addContainerProperty("subName", String.class, "");
          contFinalGrade.addContainerProperty("term", String.class, "");
          contFinalGrade.addContainerProperty("studyPoints", BigDecimal.class, null);
          contFinalGrade.addContainerProperty("grade", String.class, "");
  </code></pre>
  
  <p>and I add items by using the code below: </p>
  
  <pre><code>Item newItem = contFinalGrade.getItem(contFinalGrade.addItem());
  </code></pre>
  
  <p>I'm wondering how to get the itemId using parentCourseId. I need to get it because I need to set the parent of some items. Thanks! </p>