code: public static boolean dropIndex (Connection conn, String table, String cname, String iname)
          throws SQLException
      {
          if (!tableContainsIndex(conn, table, cname, iname)) {
              return false;
          }
  
          String update = "ALTER TABLE " + table + " DROP INDEX " + iname;
          PreparedStatement stmt = null;
          try {
              stmt = conn.prepareStatement(update);
              if (stmt.executeUpdate() == 1) {
                  log.info("Database index '" + iname + "' removed from table '" + table + "'.");
              }
          } finally {
              close(stmt);
          }
          return true;
      }
docs: Removes a named index from the specified table.
  
  @return true if the index was dropped, false if it did not exist in the first place.