@Override
  public int hashCode() {
    final int prime = 31;
    int result = 1;
    result = prime * result + ((typeName == null) ? 0 : typeName.hashCode());
    return result;
  }
Returns the category of this TypeInfo.
serde/src/java/org/apache/hadoop/hive/serde2/typeinfo/PrimitiveTypeInfo.java