code: public static boolean isIntLiteral(final RexNode rexNode)
    {
      return rexNode instanceof RexLiteral && SqlTypeName.INT_TYPES.contains(rexNode.getType().getSqlTypeName());
    }
docs: Checks if a RexNode is a literal int or not. If this returns true, then {@code RexLiteral.intValue(literal)} can be
  used to get the value of the literal.
  
  @param rexNode the node
  
  @return true if this is an int