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;
  
  import java.util.ArrayList;
  import java.util.HashMap;
  import java.util.List;
  import java.util.Map;
  import java.util.Set;
  
  import com.puppycrawl.tools.checkstyle.api.CheckstyleException;
  import com.puppycrawl.tools.checkstyle.api.Configuration;
  import com.puppycrawl.tools.checkstyle.utils.CommonUtil;
  
  /**
   * Default implementation of the Configuration interface.
   */
  public final class DefaultConfiguration implements Configuration {
  
      /** A unique serial version identifier. */
      private static final long serialVersionUID = 1157875385356127169L;
  
      /** Constant for optimization. */
      private static final Configuration[] EMPTY_CONFIGURATION_ARRAY = new Configuration[0];
  
      /** The name of this configuration. */
      private final String name;
  
      /** The list of child Configurations. */
      private final List<Configuration> children = new ArrayList<>();
  
      /** The map from property names to property values. */
      private final Map<String, String> propertyMap = new HashMap<>();
  
      /** The map containing custom messages. */
      private final Map<String, String> messages = new HashMap<>();
  
      /** The thread mode configuration. */
      private final ThreadModeSettings threadModeSettings;
  
      /**
       * Instantiates a DefaultConfiguration.
       *
       * @param name the name for this DefaultConfiguration.
       */
      public DefaultConfiguration(String name) {
          this(name, ThreadModeSettings.SINGLE_THREAD_MODE_INSTANCE);
      }
  
      /**
       * Instantiates a DefaultConfiguration.
       *
       * @param name the name for this DefaultConfiguration.
       * @param threadModeSettings the thread mode configuration.
       */
      public DefaultConfiguration(String name,
          ThreadModeSettings threadModeSettings) {
          this.name = name;
          this.threadModeSettings = threadModeSettings;
      }
  
      @Override
      public String[] getAttributeNames() {
          return getPropertyNames();
      }
  
      @Override
      public String getAttribute(String attributeName) throws CheckstyleException {
          return getProperty(attributeName);
      }
  
      @Override
      public String[] getPropertyNames() {
          final Set<String> keySet = propertyMap.keySet();
          return keySet.toArray(CommonUtil.EMPTY_STRING_ARRAY);
      }
  
      @Override
      public String getProperty(String propertyName) throws CheckstyleException {
          if (!propertyMap.containsKey(propertyName)) {
              throw new CheckstyleException(
                      "missing key '" + propertyName + "' in " + name);
          }
          return propertyMap.get(propertyName);
      }
  
      @Override
      public Configuration[] getChildren() {
          return children.toArray(
                  EMPTY_CONFIGURATION_ARRAY);
      }
  
      @Override
      public String getName() {
          return name;
      }
  
      /**
       * Makes a configuration a child of this configuration.
       *
       * @param configuration the child configuration.
       */
      public void addChild(Configuration configuration) {
          children.add(configuration);
      }
  
      /**
       * Removes a child of this configuration.
       *
       * @param configuration the child configuration to remove.
       */
      public void removeChild(final Configuration configuration) {
          children.remove(configuration);
      }
  
      /**
       * Adds n property to this configuration.
       *
       * @param attributeName the name of the property.
       * @param value the value of the property.
       * @deprecated This shall be removed in future releases. Please use
       *      {@code addProperty(String propertyName, String value)} instead.
       */
      @Deprecated(since = "8.45")
      public void addAttribute(String attributeName, String value) {
          addProperty(attributeName, value);
      }
  
      /**
       * Adds n property to this configuration.
       *
       * @param propertyName the name of the property.
       * @param value the value of the property.
       */
      public void addProperty(String propertyName, String value) {
          final String current = propertyMap.get(propertyName);
          final String newValue;
          if (current == null) {
              newValue = value;
          }
          else {
              newValue = current + "," + value;
          }
          propertyMap.put(propertyName, newValue);
      }
  
      /**
       * Adds a custom message to this configuration.
       *
       * @param key the message key
       * @param value the custom message pattern
       */
      public void addMessage(String key, String value) {
          messages.put(key, value);
      }
  
      /**
       * Returns an unmodifiable map instance containing the custom messages
       * for this configuration.
       *
       * @return unmodifiable map containing custom messages
       */
      @Override
      public Map<String, String> getMessages() {
          return new HashMap<>(messages);
      }
  
      /**
       * Gets the thread mode configuration.
       *
       * @return the thread mode configuration.
       */
      public ThreadModeSettings getThreadModeSettings() {
          return threadModeSettings;
      }
  
  }
  