@Override
    public String getTypeName() {
      StringBuilder builder = new StringBuilder(UNION_TYPE_NAME);
      builder.append("<");
      boolean first = true;
      for(ObjectInspector child: children) {
        if (first) {
          first = false;
        } else {
          builder.append(",");
        }
        builder.append(child.getTypeName());
      }
      builder.append(">");
      return builder.toString();
    }
An in-memory representation of a union type.
ql/src/java/org/apache/hadoop/hive/ql/io/orc/OrcUnion.java