code: ///////////////////////////////////////////////////////////////////////////////////////////////
  // checkstyle: Checks Java source code and other text files for adherence to a set of rules.
  // Copyright (C) 2001-2023 the original author or authors.
  //
  // This library is free software; you can redistribute it and/or
  // modify it under the terms of the GNU Lesser General Public
  // License as published by the Free Software Foundation; either
  // version 2.1 of the License, or (at your option) any later version.
  //
  // This library is distributed in the hope that it will be useful,
  // but WITHOUT ANY WARRANTY; without even the implied warranty of
  // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  // Lesser General Public License for more details.
  //
  // You should have received a copy of the GNU Lesser General Public
  // License along with this library; if not, write to the Free Software
  // Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
  ///////////////////////////////////////////////////////////////////////////////////////////////
  
  package com.puppycrawl.tools.checkstyle.filters;
  
  import java.util.HashSet;
  import java.util.Objects;
  import java.util.Set;
  import java.util.StringTokenizer;
  
  import com.puppycrawl.tools.checkstyle.utils.UnmodifiableCollectionUtil;
  
  /**
   * <p>
   * This filter element is immutable and accepts an integer that matches a CSV value, where
   * each value is an integer or a range of integers.
   * </p>
   */
  class CsvFilterElement implements IntFilterElement {
  
      /** Filter set. */
      private final Set<IntFilterElement> filters = new HashSet<>();
  
      /**
       * Constructs a {@code CsvFilterElement} from a CSV, Comma-Separated Values,
       * string. Each value is an integer, or a range of integers. A range of
       * integers is of the form integer-integer, such as 1-10.
       * Note: integers must be non-negative.
       *
       * @param pattern the CSV string.
       * @throws NumberFormatException if a component substring does not
       *     contain a parsable integer.
       */
      /* package */ CsvFilterElement(String pattern) {
          final StringTokenizer tokenizer = new StringTokenizer(pattern, ",");
          while (tokenizer.hasMoreTokens()) {
              final String token = tokenizer.nextToken().trim();
              final int index = token.indexOf('-');
              if (index == -1) {
                  final int matchValue = Integer.parseInt(token);
                  addFilter(new IntMatchFilterElement(matchValue));
              }
              else {
                  final int lowerBound =
                      Integer.parseInt(token.substring(0, index));
                  final int upperBound =
                      Integer.parseInt(token.substring(index + 1));
                  addFilter(new IntRangeFilterElement(lowerBound, upperBound));
              }
          }
      }
  
      /**
       * Adds a IntFilterElement to the set.
       *
       * @param filter the IntFilterElement to add.
       */
      private void addFilter(IntFilterElement filter) {
          filters.add(filter);
      }
  
      /**
       * Returns the IntFilters of the filter set.
       *
       * @return the IntFilters of the filter set.
       */
      protected Set<IntFilterElement> getFilters() {
          return UnmodifiableCollectionUtil.unmodifiableSet(filters);
      }
  
      /**
       * Determines whether an Integer matches a CSV integer value.
       *
       * @param intValue the Integer to check.
       * @return true if intValue is an Integer that matches a CSV value.
       */
      @Override
      public boolean accept(int intValue) {
          boolean result = false;
          for (IntFilterElement filter : getFilters()) {
              if (filter.accept(intValue)) {
                  result = true;
                  break;
              }
          }
          return result;
      }
  
      @Override
      public boolean equals(Object object) {
          if (this == object) {
              return true;
          }
          if (object == null || getClass() != object.getClass()) {
              return false;
          }
          final CsvFilterElement csvFilter = (CsvFilterElement) object;
          return Objects.equals(filters, csvFilter.filters);
      }
  
      @Override
      public int hashCode() {
          return Objects.hash(filters);
      }
  
  }
  