code: boolean isDisplayNameUnique(String displayName, String currentJobName) {
          Collection<TopLevelItem> itemCollection = items.values();
  
          // if there are a lot of projects, we'll have to store their
          // display names in a HashSet or something for a quick check
          for(TopLevelItem item : itemCollection) {
              if(item.getName().equals(currentJobName)) {
                  // we won't compare the candidate displayName against the current
                  // item. This is to prevent an validation warning if the user
                  // sets the displayName to what the existing display name is
                  continue;
              }
              else if(displayName.equals(item.getDisplayName())) {
                  return false;
              }
          }
  
          return true;
      }
docs: This method checks all existing jobs to see if displayName is
  unique. It does not check the displayName against the displayName of the
  job that the user is configuring though to prevent a validation warning
  if the user sets the displayName to what it currently is.
  @param displayName
  @param currentJobName