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.indentation;
  
  import com.puppycrawl.tools.checkstyle.api.DetailAST;
  import com.puppycrawl.tools.checkstyle.api.TokenTypes;
  import com.puppycrawl.tools.checkstyle.utils.TokenUtil;
  
  /**
   * Handler for if statements.
   *
   */
  public class IfHandler extends BlockParentHandler {
  
      /**
       * Construct an instance of this handler with the given indentation check,
       * abstract syntax tree, and parent handler.
       *
       * @param indentCheck   the indentation check
       * @param ast           the abstract syntax tree
       * @param parent        the parent handler
       */
      public IfHandler(IndentationCheck indentCheck,
          DetailAST ast, AbstractExpressionHandler parent) {
          super(indentCheck, "if", ast, parent);
      }
  
      @Override
      public IndentLevel getSuggestedChildIndent(AbstractExpressionHandler child) {
          final IndentLevel result;
          if (child instanceof ElseHandler) {
              result = getIndent();
          }
          else {
              result = super.getSuggestedChildIndent(child);
          }
          return result;
      }
  
      @Override
      protected IndentLevel getIndentImpl() {
          final IndentLevel result;
          if (isIfAfterElse()) {
              result = getParent().getIndent();
          }
          else {
              result = super.getIndentImpl();
          }
          return result;
      }
  
      /**
       * Determines if this 'if' statement is part of an 'else' clause
       * and on the same line.
       *
       * @return true if this 'if' is part of an 'else', false otherwise
       */
      private boolean isIfAfterElse() {
          // check if there is an 'else' and an 'if' on the same line
          final DetailAST parent = getMainAst().getParent();
          return parent.getType() == TokenTypes.LITERAL_ELSE
              && TokenUtil.areOnSameLine(parent, getMainAst());
      }
  
      @Override
      protected void checkTopLevelToken() {
          if (!isIfAfterElse()) {
              super.checkTopLevelToken();
          }
      }
  
      /**
       * Check the indentation of the conditional expression.
       */
      private void checkCondExpr() {
          final DetailAST condAst = getMainAst().findFirstToken(TokenTypes.LPAREN)
              .getNextSibling();
          final IndentLevel expected =
              new IndentLevel(getIndent(), getBasicOffset());
          checkExpressionSubtree(condAst, expected, false, false);
      }
  
      @Override
      public void checkIndentation() {
          super.checkIndentation();
          checkCondExpr();
          checkWrappingIndentation(getMainAst(), getIfStatementRightParen(getMainAst()));
      }
  
      /**
       * Returns right parenthesis of if statement.
       *
       * @param literalIfAst
       *          literal-if ast node(TokenTypes.LITERAL_IF)
       * @return right parenthesis of if statement.
       */
      private static DetailAST getIfStatementRightParen(DetailAST literalIfAst) {
          return literalIfAst.findFirstToken(TokenTypes.RPAREN);
      }
  
  }
  