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.annotation;
  
  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;
  import com.puppycrawl.tools.checkstyle.utils.AnnotationUtil;
  import com.puppycrawl.tools.checkstyle.utils.CheckUtil;
  
  /**
   * <p>
   * Checks that all package annotations are in the package-info.java file.
   * </p>
   * <p>
   * For Java SE8 and above, placement of package annotations in the package-info.java
   * file is enforced by the compiler and this check is not necessary.
   * </p>
   * <p>
   * For Java SE7 and below, the Java Language Specification highly recommends
   * but doesn't require that annotations are placed in the package-info.java file,
   * and this check can help to enforce that placement.
   * </p>
   * <p>
   * See <a href="https://docs.oracle.com/javase/specs/jls/se11/html/jls-7.html#jls-7.4.1">
   * Java Language Specification, &#167;7.4.1</a> for more info.
   * </p>
   * <p>
   * To configure the check:
   * </p>
   * <pre>
   * &lt;module name=&quot;PackageAnnotation&quot;/&gt;
   * </pre>
   * <p>Example of validating MyClass.java:</p>
   * <pre>
   * &#64;Deprecated
   * package com.example.annotations.packageannotation; //violation
   * </pre>
   * <p>Example of fixing violation in MyClass.java:</p>
   * <pre>
   * package com.example.annotations.packageannotation; //ok
   * </pre>
   * <p>Example of validating package-info.java:</p>
   * <pre>
   * &#64;Deprecated
   * package com.example.annotations.packageannotation; //ok
   * </pre>
   * <p>
   * Parent is {@code com.puppycrawl.tools.checkstyle.TreeWalker}
   * </p>
   * <p>
   * Violation Message Keys:
   * </p>
   * <ul>
   * <li>
   * {@code annotation.package.location}
   * </li>
   * </ul>
   *
   * @since 5.0
   */
  @StatelessCheck
  public class PackageAnnotationCheck extends AbstractCheck {
  
      /**
       * A key is pointing to the warning message text in "messages.properties"
       * file.
       */
      public static final String MSG_KEY = "annotation.package.location";
  
      @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 visitToken(final DetailAST ast) {
          final boolean containsAnnotation =
              AnnotationUtil.containsAnnotation(ast);
  
          if (containsAnnotation && !CheckUtil.isPackageInfo(getFilePath())) {
              log(ast, MSG_KEY);
          }
      }
  
  }
  