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.coding;
  
  import java.io.File;
  
  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.FullIdent;
  import com.puppycrawl.tools.checkstyle.api.TokenTypes;
  
  /**
   * <p>
   * Ensures that a class has a package declaration, and (optionally) whether
   * the package name matches the directory name for the source file.
   * </p>
   * <p>
   * Rationale: Classes that live in the null package cannot be imported.
   * Many novice developers are not aware of this.
   * </p>
   * <p>
   * Packages provide logical namespace to classes and should be stored in
   * the form of directory levels to provide physical grouping to your classes.
   * These directories are added to the classpath so that your classes
   * are visible to JVM when it runs the code.
   * </p>
   * <ul>
   * <li>
   * Property {@code matchDirectoryStructure} - Control whether to check for
   * directory and package name match.
   * Type is {@code boolean}.
   * Default value is {@code true}.
   * </li>
   * </ul>
   * <p>
   * To configure the check:
   * </p>
   * <pre>
   * &lt;module name=&quot;PackageDeclaration&quot;/&gt;
   * </pre>
   * <p>
   * Let us consider the class AnnotationLocationCheck which is in the directory
   * /com/puppycrawl/tools/checkstyle/checks/annotations/
   * </p>
   * <pre>
   * package com.puppycrawl.tools.checkstyle.checks; //Violation
   * public class AnnotationLocationCheck extends AbstractCheck {
   *   //...
   * }
   * </pre>
   * <p>
   * Example of how the check works when matchDirectoryStructure option is set to false.
   * Let us again consider the AnnotationLocationCheck class located at directory
   * /com/puppycrawl/tools/checkstyle/checks/annotations/ along with the following setup,
   * </p>
   * <pre>
   * &lt;module name=&quot;PackageDeclaration&quot;&gt;
   * &lt;property name=&quot;matchDirectoryStructure&quot; value=&quot;false&quot;/&gt;
   * &lt;/module&gt;
   * </pre>
   * <pre>
   * package com.puppycrawl.tools.checkstyle.checks;  //No Violation
   *
   * public class AnnotationLocationCheck extends AbstractCheck {
   *   //...
   * }
   * </pre>
   * <p>
   * Parent is {@code com.puppycrawl.tools.checkstyle.TreeWalker}
   * </p>
   * <p>
   * Violation Message Keys:
   * </p>
   * <ul>
   * <li>
   * {@code mismatch.package.directory}
   * </li>
   * <li>
   * {@code missing.package.declaration}
   * </li>
   * </ul>
   *
   * @since 3.2
   */
  @FileStatefulCheck
  public final class PackageDeclarationCheck extends AbstractCheck {
  
      /**
       * A key is pointing to the warning message text in "messages.properties"
       * file.
       */
      public static final String MSG_KEY_MISSING = "missing.package.declaration";
  
      /**
       * A key is pointing to the warning message text in "messages.properties"
       * file.
       */
      public static final String MSG_KEY_MISMATCH = "mismatch.package.directory";
  
      /** Is package defined. */
      private boolean defined;
  
      /** Control whether to check for directory and package name match. */
      private boolean matchDirectoryStructure = true;
  
      /**
       * Setter to control whether to check for directory and package name match.
       *
       * @param matchDirectoryStructure the new value.
       */
      public void setMatchDirectoryStructure(boolean matchDirectoryStructure) {
          this.matchDirectoryStructure = matchDirectoryStructure;
      }
  
      @Override
      public int[] getDefaultTokens() {
          return getRequiredTokens();
      }
  
      @Override
      public int[] getRequiredTokens() {
          return new int[] {TokenTypes.PACKAGE_DEF};
      }
  
      @Override
      public int[] getAcceptableTokens() {
          return getRequiredTokens();
      }
  
      @Override
      public void beginTree(DetailAST ast) {
          defined = false;
      }
  
      @Override
      public void finishTree(DetailAST ast) {
          if (!defined && ast != null) {
              log(ast, MSG_KEY_MISSING);
          }
      }
  
      @Override
      public void visitToken(DetailAST ast) {
          defined = true;
  
          if (matchDirectoryStructure) {
              final DetailAST packageNameAst = ast.getLastChild().getPreviousSibling();
              final FullIdent fullIdent = FullIdent.createFullIdent(packageNameAst);
              final String packageName = fullIdent.getText().replace('.', File.separatorChar);
  
              final String directoryName = getDirectoryName();
  
              if (!directoryName.endsWith(packageName)) {
                  log(ast, MSG_KEY_MISMATCH, packageName);
              }
          }
      }
  
      /**
       * Returns the directory name this file is in.
       *
       * @return Directory name.
       */
      private String getDirectoryName() {
          final String fileName = getFilePath();
          final int lastSeparatorPos = fileName.lastIndexOf(File.separatorChar);
          return fileName.substring(0, lastSeparatorPos);
      }
  
  }
  