code: public void setPreferredAvailabilityZones(java.util.Collection<String> preferredAvailabilityZones) {
          if (preferredAvailabilityZones == null) {
              this.preferredAvailabilityZones = null;
              return;
          }
  
          this.preferredAvailabilityZones = new com.amazonaws.internal.SdkInternalList<String>(preferredAvailabilityZones);
      }
docs: <p>
  A list of the Availability Zones in which cache nodes are created. The order of the zones in the list is not
  important.
  </p>
  <p>
  This option is only supported on Memcached.
  </p>
  <note>
  <p>
  If you are creating your cluster in an Amazon VPC (recommended) you can only locate nodes in Availability Zones
  that are associated with the subnets in the selected subnet group.
  </p>
  <p>
  The number of Availability Zones listed must equal the value of <code>NumCacheNodes</code>.
  </p>
  </note>
  <p>
  If you want all the nodes in the same Availability Zone, use <code>PreferredAvailabilityZone</code> instead, or
  repeat the Availability Zone multiple times in the list.
  </p>
  <p>
  Default: System chosen Availability Zones.
  </p>
  
  @param preferredAvailabilityZones
  A list of the Availability Zones in which cache nodes are created. The order of the zones in the list is
  not important.</p>
  <p>
  This option is only supported on Memcached.
  </p>
  <note>
  <p>
  If you are creating your cluster in an Amazon VPC (recommended) you can only locate nodes in Availability
  Zones that are associated with the subnets in the selected subnet group.
  </p>
  <p>
  The number of Availability Zones listed must equal the value of <code>NumCacheNodes</code>.
  </p>
  </note>
  <p>
  If you want all the nodes in the same Availability Zone, use <code>PreferredAvailabilityZone</code>
  instead, or repeat the Availability Zone multiple times in the list.
  </p>
  <p>
  Default: System chosen Availability Zones.