code: public static S3Objects withPrefix(AmazonS3 s3, String bucketName, String prefix) {
          S3Objects objects = new S3Objects(s3, bucketName);
          objects.prefix = prefix;
          return objects;
      }
docs: Constructs an iterable that covers the objects in an Amazon S3 bucket
  where the key begins with the given prefix.
  
  @param s3
  The Amazon S3 client.
  @param bucketName
  The bucket name.
  @param prefix
  The prefix.
  @return An iterator for object summaries.