code: public DescribeActivitiesResult withUserActivities(Activity... userActivities) {
          if (this.userActivities == null) {
              setUserActivities(new java.util.ArrayList<Activity>(userActivities.length));
          }
          for (Activity ele : userActivities) {
              this.userActivities.add(ele);
          }
          return this;
      }
docs: <p>
  The list of activities for the specified user and time period.
  </p>
  <p>
  <b>NOTE:</b> This method appends the values to the existing list (if any). Use
  {@link #setUserActivities(java.util.Collection)} or {@link #withUserActivities(java.util.Collection)} if you want
  to override the existing values.
  </p>
  
  @param userActivities
  The list of activities for the specified user and time period.
  @return Returns a reference to this object so that method calls can be chained together.