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.javadoc;
  
  import com.puppycrawl.tools.checkstyle.StatelessCheck;
  import com.puppycrawl.tools.checkstyle.api.DetailNode;
  import com.puppycrawl.tools.checkstyle.api.JavadocTokenTypes;
  import com.puppycrawl.tools.checkstyle.utils.JavadocUtil;
  
  /**
   * <p>
   * Checks that there is at least one whitespace after the leading asterisk.
   * Although spaces after asterisks are optional in the Javadoc comments, their absence
   * makes the documentation difficult to read. It is the de facto standard to put at least
   * one whitespace after the leading asterisk.
   * </p>
   * <ul>
   * <li>
   * Property {@code violateExecutionOnNonTightHtml} - Control when to print violations
   * if the Javadoc being examined by this check violates the tight html rules defined at
   * <a href="https://checkstyle.org/writingjavadocchecks.html#Tight-HTML_rules">Tight-HTML Rules</a>.
   * Type is {@code boolean}.
   * Default value is {@code false}.
   * </li>
   * </ul>
   * <p>
   * To configure the default check:
   * </p>
   * <pre>
   * &lt;module name="JavadocMissingWhitespaceAfterAsterisk"/&gt;
   * </pre>
   * <p>
   * Code Example:
   * </p>
   * <pre>
   * &#47;** This is valid single-line Javadoc. *&#47;
   * class TestClass {
   *   &#47;**
   *     *This is invalid Javadoc.
   *     *&#47;
   *   int invalidJavaDoc;
   *   &#47;**
   *     * This is valid Javadoc.
   *     *&#47;
   *   void validJavaDocMethod() {
   *   }
   *   &#47;**This is invalid single-line Javadoc. *&#47;
   *   void invalidSingleLineJavaDocMethod() {
   *   }
   *   &#47;** This is valid single-line Javadoc. *&#47;
   *   void validSingleLineJavaDocMethod() {
   *   }
   * }
   * </pre>
   * <p>
   * Parent is {@code com.puppycrawl.tools.checkstyle.TreeWalker}
   * </p>
   * <p>
   * Violation Message Keys:
   * </p>
   * <ul>
   * <li>
   * {@code javadoc.missed.html.close}
   * </li>
   * <li>
   * {@code javadoc.missing.whitespace}
   * </li>
   * <li>
   * {@code javadoc.parse.rule.error}
   * </li>
   * <li>
   * {@code javadoc.wrong.singleton.html.tag}
   * </li>
   * </ul>
   *
   * @since 8.32
   */
  @StatelessCheck
  public class JavadocMissingWhitespaceAfterAsteriskCheck extends AbstractJavadocCheck {
  
      /**
       * A key is pointing to the warning message text in "messages.properties" file.
       */
      public static final String MSG_KEY = "javadoc.missing.whitespace";
  
      @Override
      public int[] getDefaultJavadocTokens() {
          return new int[] {
              JavadocTokenTypes.JAVADOC,
              JavadocTokenTypes.LEADING_ASTERISK,
          };
      }
  
      @Override
      public int[] getRequiredJavadocTokens() {
          return getAcceptableJavadocTokens();
      }
  
      @Override
      public void visitJavadocToken(DetailNode detailNode) {
          final DetailNode textNode;
  
          if (detailNode.getType() == JavadocTokenTypes.JAVADOC) {
              textNode = JavadocUtil.getFirstChild(detailNode);
          }
          else {
              textNode = JavadocUtil.getNextSibling(detailNode);
          }
  
          if (textNode != null && textNode.getType() != JavadocTokenTypes.EOF) {
              final String text = textNode.getText();
              final int lastAsteriskPosition = getLastLeadingAsteriskPosition(text);
  
              if (!isLast(lastAsteriskPosition, text)
                      && !Character.isWhitespace(text.charAt(lastAsteriskPosition + 1))) {
                  log(textNode.getLineNumber(), textNode.getColumnNumber(), MSG_KEY);
              }
          }
      }
  
      /**
       * Checks if the character position is the last one of the string.
       *
       * @param position the position of the character
       * @param text String literal.
       * @return true if the character position is the last one of the string.
       *
       */
      private static boolean isLast(int position, String text) {
          return position == text.length() - 1;
      }
  
      /**
       * Finds the position of the last leading asterisk in the string.
       * If {@code text} contains no leading asterisk, -1 will be returned.
       *
       * @param text String literal.
       * @return the index of the last leading asterisk.
       *
       */
      private static int getLastLeadingAsteriskPosition(String text) {
          int index = -1;
  
          for (int i = 0; i < text.length(); i++) {
              if (text.charAt(i) != '*') {
                  break;
              }
              index++;
          }
  
          return index;
      }
  
  }
  