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 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.CommonUtil;
  
  /**
   * <p>
   * Checks that long constants are defined with an upper ell. That is {@code 'L'}
   * and not {@code 'l'}. This is in accordance with the Java Language Specification,
   * <a href="https://docs.oracle.com/javase/specs/jls/se11/html/jls-3.html#jls-3.10.1">
   * Section 3.10.1</a>.
   * </p>
   * <p>
   * Rationale: The lower-case ell {@code 'l'} looks a lot like {@code 1}.
   * </p>
   * <p>
   * To configure the check:
   * </p>
   * <pre>
   * &lt;module name=&quot;UpperEll&quot;/&gt;
   * </pre>
   * <pre>
   * class Test {
   *   long var1 = 508987; // OK
   *   long var2 = 508987l; // violation
   *   long var3 = 508987L; // OK
   * }
   * </pre>
   * <p>
   * Parent is {@code com.puppycrawl.tools.checkstyle.TreeWalker}
   * </p>
   * <p>
   * Violation Message Keys:
   * </p>
   * <ul>
   * <li>
   * {@code upperEll}
   * </li>
   * </ul>
   *
   * @since 3.0
   */
  @StatelessCheck
  public class UpperEllCheck extends AbstractCheck {
  
      /**
       * A key is pointing to the warning message text in "messages.properties"
       * file.
       */
      public static final String MSG_KEY = "upperEll";
  
      @Override
      public int[] getDefaultTokens() {
          return getRequiredTokens();
      }
  
      @Override
      public int[] getAcceptableTokens() {
          return getRequiredTokens();
      }
  
      @Override
      public int[] getRequiredTokens() {
          return new int[] {TokenTypes.NUM_LONG};
      }
  
      @Override
      public void visitToken(DetailAST ast) {
          if (CommonUtil.endsWithChar(ast.getText(), 'l')) {
              log(ast, MSG_KEY);
          }
      }
  
  }
  