@Explain(displayName = "columnExprMap", jsonOnly = true)
  public Map<String, String> getColumnExprMapForExplain() {
    if (this.colExprMap == null) {
      return null;
    }
    Map<String, String> colExprMapForExplain = new HashMap<>();
    for(String col:this.colExprMap.keySet()) {
      colExprMapForExplain.put(col, this.colExprMap.get(col).getExprString());
    }
    return colExprMapForExplain;
  }
The default implementation delegates to {@link #equals(Object)}. Intended to be
overridden by sub classes.
ql/src/java/org/apache/hadoop/hive/ql/plan/AbstractOperatorDesc.java