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 java.util.SortedMap;
  import java.util.TreeMap;
  
  import com.puppycrawl.tools.checkstyle.api.DetailAST;
  import com.puppycrawl.tools.checkstyle.utils.CommonUtil;
  
  /**
   * Represents a set of abstract syntax tree.
   *
   */
  public class DetailAstSet {
  
      /**
       * The instance of {@code IndentationCheck} used by this class.
       */
      private final IndentationCheck indentCheck;
  
      /**
       * Maps line numbers to their ast.
       */
      private final SortedMap<Integer, DetailAST> astLines = new TreeMap<>();
  
      /**
       * Construct an instance of this class with {@code IndentationCheck} parameters.
       *
       * @param indentCheck IndentationCheck parameters
       */
      public DetailAstSet(IndentationCheck indentCheck) {
          this.indentCheck = indentCheck;
      }
  
      /**
       * Add ast to the set of ast.
       *
       * @param ast   the ast to add
       */
      public void addAst(DetailAST ast) {
          addLineWithAst(ast.getLineNo(), ast);
      }
  
      /**
       * Map ast with their line number.
       *
       * @param lineNo    line number of ast to add
       * @param ast       ast to add
       */
      private void addLineWithAst(int lineNo, DetailAST ast) {
          astLines.put(lineNo, ast);
      }
  
      /**
       * Get starting column number for the ast.
       *
       * @param lineNum the line number as key
       * @return start column for ast
       */
      public Integer getStartColumn(int lineNum) {
          Integer startColumn = null;
          final DetailAST ast = getAst(lineNum);
  
          if (ast != null) {
              startColumn = expandedTabsColumnNo(ast);
          }
  
          return startColumn;
      }
  
      /**
       * Check if this set of ast is empty.
       *
       * @return true if empty, false otherwise
       */
      public boolean isEmpty() {
          return astLines.isEmpty();
      }
  
      /**
       * The first line in set of ast.
       *
       * @return first line in set of ast.
       */
      public DetailAST firstLine() {
          return astLines.get(astLines.firstKey());
      }
  
      /**
       * Get the ast corresponding to line number.
       *
       * @param lineNum   line number of ast.
       * @return          ast with their corresponding line number or null if no mapping is present
       */
      public DetailAST getAst(int lineNum) {
          return astLines.get(lineNum);
      }
  
      /**
       * Get the line number of the last line.
       *
       * @return the line number of the last line
       */
      public Integer lastLine() {
          return astLines.lastKey();
      }
  
      /**
       * Get the column number for the start of a given expression, expanding
       * tabs out into spaces in the process.
       *
       * @param ast   the expression to find the start of
       *
       * @return the column number for the start of the expression
       */
      protected final int expandedTabsColumnNo(DetailAST ast) {
          final String line =
              indentCheck.getLine(ast.getLineNo() - 1);
  
          return CommonUtil.lengthExpandedTabs(line, ast.getColumnNo(),
              indentCheck.getIndentationTabWidth());
      }
  
  }
  