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.whitespace;
  
  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;
  import com.puppycrawl.tools.checkstyle.utils.CodePointUtil;
  import com.puppycrawl.tools.checkstyle.utils.CommonUtil;
  
  /**
   * <p>
   * Checks that there is no whitespace before a token.
   * More specifically, it checks that it is not preceded with whitespace,
   * or (if linebreaks are allowed) all characters on the line before are
   * whitespace. To allow linebreaks before a token, set property
   * {@code allowLineBreaks} to {@code true}. No check occurs before semicolons in empty
   * for loop initializers or conditions.
   * </p>
   * <ul>
   * <li>
   * Property {@code allowLineBreaks} - Control whether whitespace is allowed
   * if the token is at a linebreak.
   * Type is {@code boolean}.
   * Default value is {@code false}.
   * </li>
   * <li>
   * Property {@code tokens} - tokens to check
   * Type is {@code java.lang.String[]}.
   * Validation type is {@code tokenSet}.
   * Default value is:
   * <a href="https://checkstyle.org/apidocs/com/puppycrawl/tools/checkstyle/api/TokenTypes.html#COMMA">
   * COMMA</a>,
   * <a href="https://checkstyle.org/apidocs/com/puppycrawl/tools/checkstyle/api/TokenTypes.html#SEMI">
   * SEMI</a>,
   * <a href="https://checkstyle.org/apidocs/com/puppycrawl/tools/checkstyle/api/TokenTypes.html#POST_INC">
   * POST_INC</a>,
   * <a href="https://checkstyle.org/apidocs/com/puppycrawl/tools/checkstyle/api/TokenTypes.html#POST_DEC">
   * POST_DEC</a>,
   * <a href="https://checkstyle.org/apidocs/com/puppycrawl/tools/checkstyle/api/TokenTypes.html#ELLIPSIS">
   * ELLIPSIS</a>,
   * <a href="https://checkstyle.org/apidocs/com/puppycrawl/tools/checkstyle/api/TokenTypes.html#LABELED_STAT">
   * LABELED_STAT</a>.
   * </li>
   * </ul>
   * <p>
   * To configure the check:
   * </p>
   * <pre>
   * &lt;module name=&quot;NoWhitespaceBefore&quot;/&gt;
   * </pre>
   * <p>Example:</p>
   * <pre>
   * int foo;
   * foo ++; // violation, whitespace before '++' is not allowed
   * foo++; // OK
   * for (int i = 0 ; i &lt; 5; i++) {}  // violation
   *            // ^ whitespace before ';' is not allowed
   * for (int i = 0; i &lt; 5; i++) {} // OK
   * int[][] array = { { 1, 2 }
   *                 , { 3, 4 } }; // violation, whitespace before ',' is not allowed
   * int[][] array2 = { { 1, 2 },
   *                    { 3, 4 } }; // OK
   * Lists.charactersOf("foo").listIterator()
   *        .forEachRemaining(System.out::print)
   *        ; // violation, whitespace before ';' is not allowed
   *   {
   *     label1 : // violation, whitespace before ':' is not allowed
   *     for (int i = 0; i &lt; 10; i++) {}
   *   }
   *
   *   {
   *     label2: // OK
   *     while (true) {}
   *   }
   * </pre>
   * <p>To configure the check to allow linebreaks before default tokens:</p>
   * <pre>
   * &lt;module name=&quot;NoWhitespaceBefore&quot;&gt;
   *   &lt;property name=&quot;allowLineBreaks&quot; value=&quot;true&quot;/&gt;
   * &lt;/module&gt;
   * </pre>
   * <p>Example:</p>
   * <pre>
   * int[][] array = { { 1, 2 }
   *                 , { 3, 4 } }; // OK, linebreak is allowed before ','
   * int[][] array2 = { { 1, 2 },
   *                    { 3, 4 } }; // OK, ideal code
   * void ellipsisExample(String ...params) {}; // violation, whitespace before '...' is not allowed
   * void ellipsisExample2(String
   *                         ...params) {}; //OK, linebreak is allowed before '...'
   * Lists.charactersOf("foo")
   *        .listIterator()
   *        .forEachRemaining(System.out::print); // OK
   * </pre>
   * <p>
   *     To Configure the check to restrict the use of whitespace before METHOD_REF and DOT tokens:
   * </p>
   * <pre>
   * &lt;module name=&quot;NoWhitespaceBefore&quot;&gt;
   *   &lt;property name=&quot;tokens&quot; value=&quot;METHOD_REF&quot;/&gt;
   *   &lt;property name=&quot;tokens&quot; value=&quot;DOT&quot;/&gt;
   * &lt;/module&gt;
   * </pre>
   * <p>Example:</p>
   * <pre>
   * Lists.charactersOf("foo").listIterator()
   *        .forEachRemaining(System.out::print); // violation, whitespace before '.' is not allowed
   * Lists.charactersOf("foo").listIterator().forEachRemaining(System.out ::print); // violation,
   *                           // whitespace before '::' is not allowed  ^
   * Lists.charactersOf("foo").listIterator().forEachRemaining(System.out::print); // OK
   * </pre>
   * <p>
   *     To configure the check to allow linebreak before METHOD_REF and DOT tokens:
   * </p>
   * <pre>
   * &lt;module name=&quot;NoWhitespaceBefore&quot;&gt;
   *   &lt;property name=&quot;tokens&quot; value=&quot;METHOD_REF&quot;/&gt;
   *   &lt;property name=&quot;tokens&quot; value=&quot;DOT&quot;/&gt;
   *   &lt;property name=&quot;allowLineBreaks&quot; value=&quot;true&quot;/&gt;
   * &lt;/module&gt;
   * </pre>
   * <p>Example:</p>
   * <pre>
   * Lists .charactersOf("foo") //violation, whitespace before '.' is not allowed
   *         .listIterator()
   *         .forEachRemaining(System.out ::print); // violation,
   *                                  // ^ whitespace before '::' is not allowed
   * Lists.charactersOf("foo")
   *        .listIterator()
   *        .forEachRemaining(System.out::print); // OK
   * </pre>
   * <p>
   * Parent is {@code com.puppycrawl.tools.checkstyle.TreeWalker}
   * </p>
   * <p>
   * Violation Message Keys:
   * </p>
   * <ul>
   * <li>
   * {@code ws.preceded}
   * </li>
   * </ul>
   *
   * @since 3.0
   */
  @StatelessCheck
  public class NoWhitespaceBeforeCheck
      extends AbstractCheck {
  
      /**
       * A key is pointing to the warning message text in "messages.properties"
       * file.
       */
      public static final String MSG_KEY = "ws.preceded";
  
      /** Control whether whitespace is allowed if the token is at a linebreak. */
      private boolean allowLineBreaks;
  
      @Override
      public int[] getDefaultTokens() {
          return new int[] {
              TokenTypes.COMMA,
              TokenTypes.SEMI,
              TokenTypes.POST_INC,
              TokenTypes.POST_DEC,
              TokenTypes.ELLIPSIS,
              TokenTypes.LABELED_STAT,
          };
      }
  
      @Override
      public int[] getAcceptableTokens() {
          return new int[] {
              TokenTypes.COMMA,
              TokenTypes.SEMI,
              TokenTypes.POST_INC,
              TokenTypes.POST_DEC,
              TokenTypes.DOT,
              TokenTypes.GENERIC_START,
              TokenTypes.GENERIC_END,
              TokenTypes.ELLIPSIS,
              TokenTypes.LABELED_STAT,
              TokenTypes.METHOD_REF,
          };
      }
  
      @Override
      public int[] getRequiredTokens() {
          return CommonUtil.EMPTY_INT_ARRAY;
      }
  
      @Override
      public void visitToken(DetailAST ast) {
          final int[] line = getLineCodePoints(ast.getLineNo() - 1);
          final int columnNoBeforeToken = ast.getColumnNo() - 1;
          final boolean isFirstToken = columnNoBeforeToken == -1;
  
          if ((isFirstToken || CommonUtil.isCodePointWhitespace(line, columnNoBeforeToken))
                  && !isInEmptyForInitializerOrCondition(ast)) {
              final boolean isViolation = !allowLineBreaks
                      || !isFirstToken
                      && !CodePointUtil.hasWhitespaceBefore(columnNoBeforeToken, line);
  
              if (isViolation) {
                  log(ast, MSG_KEY, ast.getText());
              }
          }
      }
  
      /**
       * Checks that semicolon is in empty for initializer or condition.
       *
       * @param semicolonAst DetailAST of semicolon.
       * @return true if semicolon is in empty for initializer or condition.
       */
      private static boolean isInEmptyForInitializerOrCondition(DetailAST semicolonAst) {
          boolean result = false;
          final DetailAST sibling = semicolonAst.getPreviousSibling();
          if (sibling != null
                  && (sibling.getType() == TokenTypes.FOR_INIT
                          || sibling.getType() == TokenTypes.FOR_CONDITION)
                  && !sibling.hasChildren()) {
              result = true;
          }
          return result;
      }
  
      /**
       * Setter to control whether whitespace is allowed if the token is at a linebreak.
       *
       * @param allowLineBreaks whether whitespace should be
       *     flagged at line breaks.
       */
      public void setAllowLineBreaks(boolean allowLineBreaks) {
          this.allowLineBreaks = allowLineBreaks;
      }
  
  }
  