code: @SuppressWarnings("unused")
  	private String toStringRecursive() {
  		final StringBuilder sb = new StringBuilder();
  		int elements_debug_local_recounter = toString(rootIdx, sb, 0);
  		sb.append("height=").append(getHeight()).append(" root=").append(rootIdx).append(" low=")
  				.append(lowIdx).append(" high=").append(highIdx).append(" elements=").append(elements)
  				.append(" recounter=").append(elements_debug_local_recounter);
  		return sb.toString();
  	}
docs: A recursive algorithm for converting this tree into a string
  
  @return String representing human readable tree