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;
  
  import java.util.Optional;
  import java.util.Set;
  import java.util.regex.Pattern;
  
  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.FullIdent;
  import com.puppycrawl.tools.checkstyle.api.TokenTypes;
  
  /**
   * <p>
   * Detects uncommented {@code main} methods.
   * </p>
   * <p>
   * Rationale: A {@code main} method is often used for debugging purposes.
   * When debugging is finished, developers often forget to remove the method,
   * which changes the API and increases the size of the resulting class or JAR file.
   * Except for the real program entry points, all {@code main} methods
   * should be removed or commented out of the sources.
   * </p>
   * <ul>
   * <li>
   * Property {@code excludedClasses} - Specify pattern for qualified names of
   * classes which are allowed to have a {@code main} method.
   * Type is {@code java.util.regex.Pattern}.
   * Default value is {@code "^$"}.
   * </li>
   * </ul>
   * <p>
   * To configure the check:
   * </p>
   * <pre>
   * &lt;module name=&quot;UncommentedMain&quot;/&gt;
   * </pre>
   * <p>Example:</p>
   * <pre>
   * public class Game {
   *    public static void main(String... args){}   // violation
   * }
   *
   * public class Main {
   *    public static void main(String[] args){}   // violation
   * }
   *
   * public class Launch {
   *    //public static void main(String[] args){} // OK
   * }
   *
   * public class Start {
   *    public void main(){}                       // OK
   * }
   *
   * public record MyRecord1 {
   *    public void main(){}                       // violation
   * }
   *
   * public record MyRecord2 {
   *    //public void main(){}                       // OK
   * }
   *
   * </pre>
   * <p>
   * To configure the check to allow the {@code main} method for all classes with "Main" name:
   * </p>
   * <pre>
   * &lt;module name=&quot;UncommentedMain&quot;&gt;
   *   &lt;property name=&quot;excludedClasses&quot; value=&quot;\.Main$&quot;/&gt;
   * &lt;/module&gt;
   * </pre>
   * <p>Example:</p>
   * <pre>
   * public class Game {
   *    public static void main(String... args){}   // violation
   * }
   *
   * public class Main {
   *    public static void main(String[] args){}   // OK
   * }
   *
   * public class Launch {
   *    //public static void main(String[] args){} // OK
   * }
   *
   * public class Start {
   *    public void main(){}                       // OK
   * }
   *
   * public record MyRecord1 {
   *    public void main(){}                       // OK
   * }
   *
   * </pre>
   * <p>
   * Parent is {@code com.puppycrawl.tools.checkstyle.TreeWalker}
   * </p>
   * <p>
   * Violation Message Keys:
   * </p>
   * <ul>
   * <li>
   * {@code uncommented.main}
   * </li>
   * </ul>
   *
   * @since 3.2
   */
  @FileStatefulCheck
  public class UncommentedMainCheck
      extends AbstractCheck {
  
      /**
       * A key is pointing to the warning message text in "messages.properties"
       * file.
       */
      public static final String MSG_KEY = "uncommented.main";
  
      /** Set of possible String array types. */
      private static final Set<String> STRING_PARAMETER_NAMES = Set.of(
          String[].class.getCanonicalName(),
          String.class.getCanonicalName(),
          String[].class.getSimpleName(),
          String.class.getSimpleName()
      );
  
      /**
       * Specify pattern for qualified names of classes which are allowed to
       * have a {@code main} method.
       */
      private Pattern excludedClasses = Pattern.compile("^$");
      /** Current class name. */
      private String currentClass;
      /** Current package. */
      private FullIdent packageName;
      /** Class definition depth. */
      private int classDepth;
  
      /**
       * Setter to specify pattern for qualified names of classes which are allowed
       * to have a {@code main} method.
       *
       * @param excludedClasses a pattern
       */
      public void setExcludedClasses(Pattern excludedClasses) {
          this.excludedClasses = excludedClasses;
      }
  
      @Override
      public int[] getAcceptableTokens() {
          return getRequiredTokens();
      }
  
      @Override
      public int[] getDefaultTokens() {
          return getRequiredTokens();
      }
  
      @Override
      public int[] getRequiredTokens() {
          return new int[] {
              TokenTypes.METHOD_DEF,
              TokenTypes.CLASS_DEF,
              TokenTypes.PACKAGE_DEF,
              TokenTypes.RECORD_DEF,
          };
      }
  
      @Override
      public void beginTree(DetailAST rootAST) {
          packageName = FullIdent.createFullIdent(null);
          classDepth = 0;
      }
  
      @Override
      public void leaveToken(DetailAST ast) {
          if (ast.getType() == TokenTypes.CLASS_DEF) {
              classDepth--;
          }
      }
  
      @Override
      public void visitToken(DetailAST ast) {
          switch (ast.getType()) {
              case TokenTypes.PACKAGE_DEF:
                  visitPackageDef(ast);
                  break;
              case TokenTypes.RECORD_DEF:
              case TokenTypes.CLASS_DEF:
                  visitClassOrRecordDef(ast);
                  break;
              case TokenTypes.METHOD_DEF:
                  visitMethodDef(ast);
                  break;
              default:
                  throw new IllegalStateException(ast.toString());
          }
      }
  
      /**
       * Sets current package.
       *
       * @param packageDef node for package definition
       */
      private void visitPackageDef(DetailAST packageDef) {
          packageName = FullIdent.createFullIdent(packageDef.getLastChild()
                  .getPreviousSibling());
      }
  
      /**
       * If not inner class then change current class name.
       *
       * @param classOrRecordDef node for class or record definition
       */
      private void visitClassOrRecordDef(DetailAST classOrRecordDef) {
          // we are not use inner classes because they can not
          // have static methods
          if (classDepth == 0) {
              final DetailAST ident = classOrRecordDef.findFirstToken(TokenTypes.IDENT);
              currentClass = packageName.getText() + "." + ident.getText();
              classDepth++;
          }
      }
  
      /**
       * Checks method definition if this is
       * {@code public static void main(String[])}.
       *
       * @param method method definition node
       */
      private void visitMethodDef(DetailAST method) {
          if (classDepth == 1
                  // method not in inner class or in interface definition
                  && checkClassName()
                  && checkName(method)
                  && checkModifiers(method)
                  && checkType(method)
                  && checkParams(method)) {
              log(method, MSG_KEY);
          }
      }
  
      /**
       * Checks that current class is not excluded.
       *
       * @return true if check passed, false otherwise
       */
      private boolean checkClassName() {
          return !excludedClasses.matcher(currentClass).find();
      }
  
      /**
       * Checks that method name is @quot;main@quot;.
       *
       * @param method the METHOD_DEF node
       * @return true if check passed, false otherwise
       */
      private static boolean checkName(DetailAST method) {
          final DetailAST ident = method.findFirstToken(TokenTypes.IDENT);
          return "main".equals(ident.getText());
      }
  
      /**
       * Checks that method has final and static modifiers.
       *
       * @param method the METHOD_DEF node
       * @return true if check passed, false otherwise
       */
      private static boolean checkModifiers(DetailAST method) {
          final DetailAST modifiers =
              method.findFirstToken(TokenTypes.MODIFIERS);
  
          return modifiers.findFirstToken(TokenTypes.LITERAL_PUBLIC) != null
              && modifiers.findFirstToken(TokenTypes.LITERAL_STATIC) != null;
      }
  
      /**
       * Checks that return type is {@code void}.
       *
       * @param method the METHOD_DEF node
       * @return true if check passed, false otherwise
       */
      private static boolean checkType(DetailAST method) {
          final DetailAST type =
              method.findFirstToken(TokenTypes.TYPE).getFirstChild();
          return type.getType() == TokenTypes.LITERAL_VOID;
      }
  
      /**
       * Checks that method has only {@code String[]} or only {@code String...} param.
       *
       * @param method the METHOD_DEF node
       * @return true if check passed, false otherwise
       */
      private static boolean checkParams(DetailAST method) {
          boolean checkPassed = false;
          final DetailAST params = method.findFirstToken(TokenTypes.PARAMETERS);
  
          if (params.getChildCount() == 1) {
              final DetailAST parameterType = params.getFirstChild().findFirstToken(TokenTypes.TYPE);
              final boolean isArrayDeclaration =
                  parameterType.findFirstToken(TokenTypes.ARRAY_DECLARATOR) != null;
              final Optional<DetailAST> varargs = Optional.ofNullable(
                  params.getFirstChild().findFirstToken(TokenTypes.ELLIPSIS));
  
              if (isArrayDeclaration || varargs.isPresent()) {
                  checkPassed = isStringType(parameterType.getFirstChild());
              }
          }
          return checkPassed;
      }
  
      /**
       * Whether the type is java.lang.String.
       *
       * @param typeAst the type to check.
       * @return true, if the type is java.lang.String.
       */
      private static boolean isStringType(DetailAST typeAst) {
          final FullIdent type = FullIdent.createFullIdent(typeAst);
          return STRING_PARAMETER_NAMES.contains(type.getText());
      }
  
  }
  