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.io.File;
  import java.util.regex.Pattern;
  
  import com.puppycrawl.tools.checkstyle.FileStatefulCheck;
  import com.puppycrawl.tools.checkstyle.api.AbstractCheck;
  import com.puppycrawl.tools.checkstyle.api.DetailAST;
  import com.puppycrawl.tools.checkstyle.api.TokenTypes;
  import com.puppycrawl.tools.checkstyle.utils.TokenUtil;
  
  /**
   * <p>
   * Checks that the outer type name and the file name match.
   * For example, the class {@code Foo} must be in a file named {@code Foo.java}.
   * </p>
   * <p>
   * To configure the check:
   * </p>
   * <pre>
   * &lt;module name=&quot;OuterTypeFilename&quot;/&gt;
   * </pre>
   * <p>Example of class Test in a file named Test.java</p>
   * <pre>
   * public class Test { // OK
   *
   * }
   * </pre>
   * <p>Example of class Foo in a file named Test.java</p>
   * <pre>
   * class Foo { // violation
   *
   * }
   * </pre>
   * <p>Example of interface Foo in a file named Test.java</p>
   * <pre>
   * interface Foo { // violation
   *
   * }
   * </pre>
   * <p>Example of enum Foo in a file named Test.java</p>
   * <pre>
   * enum Foo { // violation
   *
   * }
   * </pre>
   * <p>Example of record Foo in a file named Test.java</p>
   * <pre>
   * record Foo { // violation
   *
   * }
   * </pre>
   * <p>
   * Parent is {@code com.puppycrawl.tools.checkstyle.TreeWalker}
   * </p>
   * <p>
   * Violation Message Keys:
   * </p>
   * <ul>
   * <li>
   * {@code type.file.mismatch}
   * </li>
   * </ul>
   *
   * @since 5.3
   */
  @FileStatefulCheck
  public class OuterTypeFilenameCheck extends AbstractCheck {
  
      /**
       * A key is pointing to the warning message text in "messages.properties"
       * file.
       */
      public static final String MSG_KEY = "type.file.mismatch";
  
      /** Pattern matching any file extension with dot included. */
      private static final Pattern FILE_EXTENSION_PATTERN = Pattern.compile("\\.[^.]*$");
  
      /** Indicates whether the first token has been seen in the file. */
      private boolean seenFirstToken;
  
      /** Current file name. */
      private String fileName;
  
      /** If file has public type. */
      private boolean hasPublic;
  
      /** Outer type with mismatched file name. */
      private DetailAST wrongType;
  
      @Override
      public int[] getDefaultTokens() {
          return getRequiredTokens();
      }
  
      @Override
      public int[] getAcceptableTokens() {
          return getRequiredTokens();
      }
  
      @Override
      public int[] getRequiredTokens() {
          return new int[] {
              TokenTypes.CLASS_DEF,
              TokenTypes.INTERFACE_DEF,
              TokenTypes.ENUM_DEF,
              TokenTypes.ANNOTATION_DEF,
              TokenTypes.RECORD_DEF,
          };
      }
  
      @Override
      public void beginTree(DetailAST rootAST) {
          fileName = getSourceFileName();
          seenFirstToken = false;
          hasPublic = false;
          wrongType = null;
      }
  
      @Override
      public void visitToken(DetailAST ast) {
          if (seenFirstToken) {
              final DetailAST modifiers = ast.findFirstToken(TokenTypes.MODIFIERS);
              if (modifiers.findFirstToken(TokenTypes.LITERAL_PUBLIC) != null
                      && TokenUtil.isRootNode(ast.getParent())) {
                  hasPublic = true;
              }
          }
          else {
              final String outerTypeName = ast.findFirstToken(TokenTypes.IDENT).getText();
  
              if (!fileName.equals(outerTypeName)) {
                  wrongType = ast;
              }
          }
          seenFirstToken = true;
      }
  
      @Override
      public void finishTree(DetailAST rootAST) {
          if (!hasPublic && wrongType != null) {
              log(wrongType, MSG_KEY);
          }
      }
  
      /**
       * Get source file name.
       *
       * @return source file name.
       */
      private String getSourceFileName() {
          String name = getFilePath();
          name = name.substring(name.lastIndexOf(File.separatorChar) + 1);
          return FILE_EXTENSION_PATTERN.matcher(name).replaceAll("");
      }
  
  }
  