public int size() {
    return fieldSchemas.size();
  }
Note : The position will be re-numbered when one of the preceding columns are removed.
Hence, the client should not cache this value and expect it to be always valid.
@param fieldName
@return the index of field named fieldName in Schema. If field is not
present, returns null.
hcatalog/core/src/main/java/org/apache/hive/hcatalog/data/schema/HCatSchema.java