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.CommonUtil;
  import com.puppycrawl.tools.checkstyle.utils.TokenUtil;
  
  /**
   * <p>
   * Checks that annotations are located on the same line with their targets.
   * Verifying with this check is not good practice, but it is using by some style guides.
   * </p>
   * <ul>
   * <li>
   * Property {@code tokens} - tokens to check
   * Type is {@code java.lang.String[]}.
   * Validation type is {@code tokenSet}.
   * Default value is:
   * <a href="https://checkstyle.org/apidocs/com/puppycrawl/tools/checkstyle/api/TokenTypes.html#CLASS_DEF">
   * CLASS_DEF</a>,
   * <a href="https://checkstyle.org/apidocs/com/puppycrawl/tools/checkstyle/api/TokenTypes.html#INTERFACE_DEF">
   * INTERFACE_DEF</a>,
   * <a href="https://checkstyle.org/apidocs/com/puppycrawl/tools/checkstyle/api/TokenTypes.html#ENUM_DEF">
   * ENUM_DEF</a>,
   * <a href="https://checkstyle.org/apidocs/com/puppycrawl/tools/checkstyle/api/TokenTypes.html#METHOD_DEF">
   * METHOD_DEF</a>,
   * <a href="https://checkstyle.org/apidocs/com/puppycrawl/tools/checkstyle/api/TokenTypes.html#CTOR_DEF">
   * CTOR_DEF</a>,
   * <a href="https://checkstyle.org/apidocs/com/puppycrawl/tools/checkstyle/api/TokenTypes.html#VARIABLE_DEF">
   * VARIABLE_DEF</a>,
   * <a href="https://checkstyle.org/apidocs/com/puppycrawl/tools/checkstyle/api/TokenTypes.html#RECORD_DEF">
   * RECORD_DEF</a>,
   * <a href="https://checkstyle.org/apidocs/com/puppycrawl/tools/checkstyle/api/TokenTypes.html#COMPACT_CTOR_DEF">
   * COMPACT_CTOR_DEF</a>.
   * </li>
   * </ul>
   * <p>
   * To configure the check:
   * </p>
   * <pre>
   * &lt;module name=&quot;AnnotationOnSameLine&quot;/&gt;
   * </pre>
   * <p>
   * Example:
   * </p>
   * <pre>
   * class Foo {
   *
   *   &#64;SuppressWarnings("deprecation")  // violation, annotation should be on the same line
   *   public Foo() {
   *   }
   *
   *   &#64;SuppressWarnings("unchecked") public void fun2() {  // OK
   *   }
   *
   * }
   *
   * &#64;SuppressWarnings("unchecked") class Bar extends Foo {  // OK
   *
   *   &#64;Deprecated public Bar() {  // OK
   *   }
   *
   *   &#64;Override  // violation, annotation should be on the same line
   *   public void fun1() {
   *   }
   *
   *   &#64;Before &#64;Override public void fun2() {  // OK
   *   }
   *
   *   &#64;SuppressWarnings("deprecation")  // violation, annotation should be on the same line
   *   &#64;Before public void fun3() {
   *   }
   *
   * }
   * </pre>
   * <p>
   * To configure the check to check for annotations applied on
   * interfaces, variables and constructors:
   * </p>
   * <pre>
   * &lt;module name=&quot;AnnotationOnSameLine&quot;&gt;
   *   &lt;property name=&quot;tokens&quot;
   *       value=&quot;INTERFACE_DEF, VARIABLE_DEF, CTOR_DEF&quot;/&gt;
   * &lt;/module&gt;
   * </pre>
   * <p>
   * Example:
   * </p>
   * <pre>
   * &#64;Deprecated interface Foo {  // OK
   *
   *   void doSomething();
   *
   * }
   *
   * class Bar implements Foo {
   *
   *   &#64;SuppressWarnings("deprecation")  // violation, annotation should be on the same line
   *   public Bar() {
   *   }
   *
   *   &#64;Override  // OK
   *   public void doSomething() {
   *   }
   *
   *   &#64;Nullable  // violation, annotation should be on the same line
   *   String s;
   *
   * }
   * </pre>
   * <p>
   * Parent is {@code com.puppycrawl.tools.checkstyle.TreeWalker}
   * </p>
   * <p>
   * Violation Message Keys:
   * </p>
   * <ul>
   * <li>
   * {@code annotation.same.line}
   * </li>
   * </ul>
   *
   * @since 8.2
   */
  @StatelessCheck
  public class AnnotationOnSameLineCheck extends AbstractCheck {
  
      /** A key is pointing to the warning message text in "messages.properties" file. */
      public static final String MSG_KEY_ANNOTATION_ON_SAME_LINE = "annotation.same.line";
  
      @Override
      public int[] getDefaultTokens() {
          return new int[] {
              TokenTypes.CLASS_DEF,
              TokenTypes.INTERFACE_DEF,
              TokenTypes.ENUM_DEF,
              TokenTypes.METHOD_DEF,
              TokenTypes.CTOR_DEF,
              TokenTypes.VARIABLE_DEF,
              TokenTypes.RECORD_DEF,
              TokenTypes.COMPACT_CTOR_DEF,
          };
      }
  
      @Override
      public int[] getAcceptableTokens() {
          return new int[] {
              TokenTypes.CLASS_DEF,
              TokenTypes.INTERFACE_DEF,
              TokenTypes.ENUM_DEF,
              TokenTypes.METHOD_DEF,
              TokenTypes.CTOR_DEF,
              TokenTypes.VARIABLE_DEF,
              TokenTypes.PARAMETER_DEF,
              TokenTypes.ANNOTATION_DEF,
              TokenTypes.TYPECAST,
              TokenTypes.LITERAL_THROWS,
              TokenTypes.IMPLEMENTS_CLAUSE,
              TokenTypes.TYPE_ARGUMENT,
              TokenTypes.LITERAL_NEW,
              TokenTypes.DOT,
              TokenTypes.ANNOTATION_FIELD_DEF,
              TokenTypes.RECORD_DEF,
              TokenTypes.COMPACT_CTOR_DEF,
          };
      }
  
      @Override
      public int[] getRequiredTokens() {
          return CommonUtil.EMPTY_INT_ARRAY;
      }
  
      @Override
      public void visitToken(DetailAST ast) {
          DetailAST nodeWithAnnotations = ast;
          if (ast.getType() == TokenTypes.TYPECAST) {
              nodeWithAnnotations = ast.findFirstToken(TokenTypes.TYPE);
          }
          DetailAST modifiersNode = nodeWithAnnotations.findFirstToken(TokenTypes.MODIFIERS);
          if (modifiersNode == null) {
              modifiersNode = nodeWithAnnotations.findFirstToken(TokenTypes.ANNOTATIONS);
          }
          if (modifiersNode != null) {
              for (DetailAST annotationNode = modifiersNode.getFirstChild();
                      annotationNode != null;
                      annotationNode = annotationNode.getNextSibling()) {
                  if (annotationNode.getType() == TokenTypes.ANNOTATION
                          && !TokenUtil.areOnSameLine(annotationNode, getNextNode(annotationNode))) {
                      log(annotationNode, MSG_KEY_ANNOTATION_ON_SAME_LINE,
                            getAnnotationName(annotationNode));
                  }
              }
          }
      }
  
      /**
       * Finds next node of ast tree.
       *
       * @param node current node
       * @return node that is next to given
       */
      private static DetailAST getNextNode(DetailAST node) {
          DetailAST nextNode = node.getNextSibling();
          if (nextNode == null) {
              nextNode = node.getParent().getNextSibling();
          }
          return nextNode;
      }
  
      /**
       * Returns the name of the given annotation.
       *
       * @param annotation annotation node.
       * @return annotation name.
       */
      private static String getAnnotationName(DetailAST annotation) {
          DetailAST identNode = annotation.findFirstToken(TokenTypes.IDENT);
          if (identNode == null) {
              identNode = annotation.findFirstToken(TokenTypes.DOT).getLastChild();
          }
          return identNode.getText();
      }
  
  }
  