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 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;
  
  /**
   * <p>
   * Restricts nested {@code for} blocks to a specified depth.
   * </p>
   * <ul>
   * <li>
   * Property {@code max} - Specify maximum allowed nesting depth.
   * Type is {@code int}.
   * Default value is {@code 1}.
   * </li>
   * </ul>
   * <p>
   * To configure the check:
   * </p>
   * <pre>
   * &lt;module name=&quot;NestedForDepth&quot;/&gt;
   * </pre>
   * <p>Example:</p>
   * <pre>
   * for(int i=0; i&lt;10; i++) {
   *   for(int j=0; j&lt;i; j++) {
   *     for(int k=0; k&lt;j; k++) { // violation, max allowed nested loop number is 1
   *     }
   *   }
   * }
   *
   * for(int i=0; i&lt;10; i++) {
   *   for(int j=0; j&lt;i; j++) { // ok
   *   }
   * }
   * </pre>
   * <p>
   * To configure the check to allow nesting depth 2:
   * </p>
   * <pre>
   * &lt;module name=&quot;NestedForDepth&quot;&gt;
   *   &lt;property name=&quot;max&quot; value=&quot;2&quot;/&gt;
   * &lt;/module&gt;
   * </pre>
   * <p>Example:</p>
   * <pre>
   * for(int i=0; i&lt;10; i++) {
   *   for(int j=0; j&lt;i; j++) {
   *     for(int k=0; k&lt;j; k++) {
   *       for(int l=0; l&lt;k; l++) { // violation, max allowed nested loop number is 2
   *       }
   *     }
   *    }
   * }
   *
   * for(int i=0; i&lt;10; i++) {
   *   for(int j=0; j&lt;i; j++) {
   *     for(int k=0; k&lt;j; k++) { // ok
   *     }
   *   }
   * }
   * </pre>
   * <p>
   * Parent is {@code com.puppycrawl.tools.checkstyle.TreeWalker}
   * </p>
   * <p>
   * Violation Message Keys:
   * </p>
   * <ul>
   * <li>
   * {@code nested.for.depth}
   * </li>
   * </ul>
   *
   * @since 5.3
   */
  @FileStatefulCheck
  public final class NestedForDepthCheck extends AbstractCheck {
  
      /**
       * A key is pointing to the warning message text in "messages.properties"
       * file.
       */
      public static final String MSG_KEY = "nested.for.depth";
  
      /** Specify maximum allowed nesting depth. */
      private int max = 1;
      /** Current nesting depth. */
      private int depth;
  
      /**
       * Setter to specify maximum allowed nesting depth.
       *
       * @param max maximum allowed nesting depth.
       */
      public void setMax(int max) {
          this.max = max;
      }
  
      @Override
      public int[] getDefaultTokens() {
          return getRequiredTokens();
      }
  
      @Override
      public int[] getAcceptableTokens() {
          return getRequiredTokens();
      }
  
      @Override
      public int[] getRequiredTokens() {
          return new int[] {TokenTypes.LITERAL_FOR};
      }
  
      @Override
      public void visitToken(DetailAST ast) {
          if (depth > max) {
              log(ast, MSG_KEY, depth, max);
          }
          ++depth;
      }
  
      @Override
      public void leaveToken(DetailAST ast) {
          --depth;
      }
  
  }
  