code: static DocId create(int docNumber) {
          if (docNumber < Short.MAX_VALUE) {
              // use cached values for docNumbers up to 32k
              return LOW_DOC_IDS[docNumber];
          }
          else
          {
              return new PlainDocId(docNumber);
          }
      }
docs: Creates a <code>DocId</code> based on a document number.
  
  @param docNumber the document number.
  @return a <code>DocId</code> based on a document number.