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.StatelessCheck;
  import com.puppycrawl.tools.checkstyle.api.AbstractCheck;
  import com.puppycrawl.tools.checkstyle.api.DetailAST;
  import com.puppycrawl.tools.checkstyle.api.TokenTypes;
  
  /**
   * <p>
   * Checks that classes (except abstract ones) define a constructor and don't rely
   * on the default one.
   * </p>
   * <p>
   * To configure the check:
   * </p>
   * <pre>
   * &lt;module name=&quot;MissingCtor&quot;/&gt;
   * </pre>
   * <p>Example:</p>
   * <pre>
   * class ExampleOk { // OK
   *   private int a;
   *   ExampleOk(int a) {
   *     this.a = a;
   *   }
   * }
   * class ExampleDefaultCtor { // OK
   *   private String s;
   *   ExampleDefaultCtor() {
   *     s = "foobar";
   *   }
   * }
   * class InvalidExample { // violation, class must have a constructor.
   *   public void test() {}
   * }
   * abstract class AbstractExample { // OK
   *   public abstract void test() {}
   * }
   * </pre>
   * <p>
   * Parent is {@code com.puppycrawl.tools.checkstyle.TreeWalker}
   * </p>
   * <p>
   * Violation Message Keys:
   * </p>
   * <ul>
   * <li>
   * {@code missing.ctor}
   * </li>
   * </ul>
   *
   * @since 3.4
   */
  @StatelessCheck
  public class MissingCtorCheck extends AbstractCheck {
  
      /**
       * A key is pointing to the warning message text in "messages.properties"
       * file.
       */
      public static final String MSG_KEY = "missing.ctor";
  
      @Override
      public int[] getDefaultTokens() {
          return getRequiredTokens();
      }
  
      @Override
      public int[] getAcceptableTokens() {
          return getRequiredTokens();
      }
  
      @Override
      public int[] getRequiredTokens() {
          return new int[] {TokenTypes.CLASS_DEF};
      }
  
      @Override
      public void visitToken(DetailAST ast) {
          final DetailAST modifiers = ast.findFirstToken(TokenTypes.MODIFIERS);
          if (modifiers.findFirstToken(TokenTypes.ABSTRACT) == null
                  && ast.findFirstToken(TokenTypes.OBJBLOCK)
                      .findFirstToken(TokenTypes.CTOR_DEF) == null) {
              log(ast, MSG_KEY);
          }
      }
  
  }
  