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.checks;
  
  import java.util.regex.Pattern;
  
  import com.puppycrawl.tools.checkstyle.StatelessCheck;
  import com.puppycrawl.tools.checkstyle.api.AbstractCheck;
  import com.puppycrawl.tools.checkstyle.api.DetailAST;
  import com.puppycrawl.tools.checkstyle.api.TokenTypes;
  
  /**
   * <p>
   * Checks for {@code TODO:} comments. Actually it is a generic
   * <a href="https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/util/regex/Pattern.html">
   * pattern</a> matcher on Java comments. To check for other patterns
   * in Java comments, set the {@code format} property.
   * </p>
   * <p>
   * Using {@code TODO:} comments is a great way to keep track of tasks that need to be done.
   * Having them reported by Checkstyle makes it very hard to forget about them.
   * </p>
   * <ul>
   * <li>
   * Property {@code format} - Specify pattern to match comments against.
   * Type is {@code java.util.regex.Pattern}.
   * Default value is {@code "TODO:"}.
   * </li>
   * </ul>
   * <p>
   * To configure the check:
   * </p>
   * <pre>
   * &lt;module name="TodoComment"/&gt;
   * </pre>
   * <p>
   * Example:
   * </p>
   * <pre>
   * i++; // TODO: do differently in future   // violation
   * i++; // todo: do differently in future   // OK
   * </pre>
   * <p>
   * To configure the check for comments that contain {@code TODO} and {@code FIXME}:
   * </p>
   * <pre>
   * &lt;module name="TodoComment"&gt;
   *   &lt;property name="format" value="(TODO)|(FIXME)"/&gt;
   * &lt;/module&gt;
   * </pre>
   * <p>
   * Example:
   * </p>
   * <pre>
   * i++;   // TODO: do differently in future   // violation
   * i++;   // todo: do differently in future   // OK
   * i=i/x; // FIXME: handle x = 0 case         // violation
   * i=i/x; // FIX :  handle x = 0 case         // OK
   * </pre>
   * <p>
   * Parent is {@code com.puppycrawl.tools.checkstyle.TreeWalker}
   * </p>
   * <p>
   * Violation Message Keys:
   * </p>
   * <ul>
   * <li>
   * {@code todo.match}
   * </li>
   * </ul>
   *
   * @since 3.0
   */
  @StatelessCheck
  public class TodoCommentCheck
          extends AbstractCheck {
  
      /**
       * A key is pointing to the warning message text in "messages.properties"
       * file.
       */
      public static final String MSG_KEY = "todo.match";
  
      /**
       * Specify pattern to match comments against.
       */
      private Pattern format = Pattern.compile("TODO:");
  
      @Override
      public boolean isCommentNodesRequired() {
          return true;
      }
  
      /**
       * Setter to specify pattern to match comments against.
       *
       * @param pattern
       *        pattern of 'todo' comment.
       */
      public void setFormat(Pattern pattern) {
          format = pattern;
      }
  
      @Override
      public int[] getDefaultTokens() {
          return getRequiredTokens();
      }
  
      @Override
      public int[] getAcceptableTokens() {
          return getRequiredTokens();
      }
  
      @Override
      public int[] getRequiredTokens() {
          return new int[] {TokenTypes.COMMENT_CONTENT };
      }
  
      @Override
      public void visitToken(DetailAST ast) {
          final String[] lines = ast.getText().split("\n");
  
          for (String line : lines) {
              if (format.matcher(line).find()) {
                  log(ast, MSG_KEY, format.pattern());
              }
          }
      }
  
  }
  