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.design;
  
  import java.util.BitSet;
  
  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.ScopeUtil;
  import com.puppycrawl.tools.checkstyle.utils.TokenUtil;
  
  /**
   * <p>
   * Checks nested (internal) classes/interfaces are declared at the bottom of the
   * primary (top-level) class after all init and static init blocks,
   * method, constructor and field declarations.
   * </p>
   * <p>
   * To configure the check:
   * </p>
   * <pre>
   * &lt;module name=&quot;InnerTypeLast&quot;/&gt;
   * </pre>
   * <p>Example:</p>
   * <pre>
   * class Test {
   *     private String s; // OK
   *     class InnerTest1 {}
   *     public void test() {} // violation, method should be declared before inner types.
   * }
   *
   * class Test2 {
   *     static {}; // OK
   *     class InnerTest1 {}
   *     public Test2() {} // violation, constructor should be declared before inner types.
   * }
   *
   * class Test3 {
   *     private String s; // OK
   *     public void test() {} // OK
   *     class InnerTest1 {}
   * }
   * </pre>
   * <p>
   * Parent is {@code com.puppycrawl.tools.checkstyle.TreeWalker}
   * </p>
   * <p>
   * Violation Message Keys:
   * </p>
   * <ul>
   * <li>
   * {@code arrangement.members.before.inner}
   * </li>
   * </ul>
   *
   * @since 5.2
   */
  @FileStatefulCheck
  public class InnerTypeLastCheck extends AbstractCheck {
  
      /**
       * A key is pointing to the warning message text in "messages.properties"
       * file.
       */
      public static final String MSG_KEY = "arrangement.members.before.inner";
  
      /** Set of class member tokens. */
      private static final BitSet CLASS_MEMBER_TOKENS = TokenUtil.asBitSet(
              TokenTypes.VARIABLE_DEF,
              TokenTypes.METHOD_DEF,
              TokenTypes.CTOR_DEF,
              TokenTypes.INSTANCE_INIT,
              TokenTypes.STATIC_INIT,
              TokenTypes.COMPACT_CTOR_DEF
      );
  
      /** Meet a root class. */
      private boolean rootClass;
  
      @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.RECORD_DEF,
          };
      }
  
      @Override
      public void beginTree(DetailAST rootAST) {
          rootClass = true;
      }
  
      @Override
      public void visitToken(DetailAST ast) {
          // First root class
          if (rootClass) {
              rootClass = false;
          }
          else {
              DetailAST nextSibling = ast;
              while (nextSibling != null) {
                  if (!ScopeUtil.isInCodeBlock(ast)
                          && CLASS_MEMBER_TOKENS.get(nextSibling.getType())) {
                      log(nextSibling, MSG_KEY);
                  }
                  nextSibling = nextSibling.getNextSibling();
              }
          }
      }
  
      @Override
      public void leaveToken(DetailAST ast) {
          if (TokenUtil.isRootNode(ast.getParent())) {
              rootClass = true;
          }
      }
  
  }
  