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.api;
  
  import java.util.concurrent.atomic.AtomicInteger;
  
  /**
   * An audit listener that counts how many {@link AuditEvent AuditEvents}
   * of a given severity have been generated.
   *
   */
  public final class SeverityLevelCounter implements AuditListener {
  
      /** The severity level to watch out for. */
      private final SeverityLevel level;
  
      /** Keeps track of the number of counted events. */
      private final AtomicInteger count = new AtomicInteger();
  
      /**
       * Creates a new counter.
       *
       * @param level the severity level events need to have, must be non-null.
       * @throws IllegalArgumentException when level is null
       */
      public SeverityLevelCounter(SeverityLevel level) {
          if (level == null) {
              throw new IllegalArgumentException("'level' cannot be null");
          }
          this.level = level;
      }
  
      @Override
      public void addError(AuditEvent event) {
          if (level == event.getSeverityLevel()) {
              count.incrementAndGet();
          }
      }
  
      @Override
      public void addException(AuditEvent event, Throwable throwable) {
          if (level == SeverityLevel.ERROR) {
              count.incrementAndGet();
          }
      }
  
      @Override
      public void auditStarted(AuditEvent event) {
          count.set(0);
      }
  
      @Override
      public void fileStarted(AuditEvent event) {
          // No code by default, should be overridden only by demand at subclasses
      }
  
      @Override
      public void auditFinished(AuditEvent event) {
          // No code by default, should be overridden only by demand at subclasses
      }
  
      @Override
      public void fileFinished(AuditEvent event) {
          // No code by default, should be overridden only by demand at subclasses
      }
  
      /**
       * Returns the number of counted events since audit started.
       *
       * @return the number of counted events since audit started.
       */
      public int getCount() {
          return count.get();
      }
  
  }
  