code: /*
   * Licensed to the Apache Software Foundation (ASF) under one or more
   * contributor license agreements.  See the NOTICE file distributed with
   * this work for additional information regarding copyright ownership.
   * The ASF licenses this file to You under the Apache License, Version 2.0
   * (the "License"); you may not use this file except in compliance with
   * the License.  You may obtain a copy of the License at
   * 
   *      http://www.apache.org/licenses/LICENSE-2.0
   * 
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  package org.apache.commons.io.comparator;
  
  import java.io.File;
  import java.io.Serializable;
  import java.util.Comparator;
  
  import org.apache.commons.io.FilenameUtils;
  import org.apache.commons.io.IOCase;
  
  /**
   * Compare the file name <b>extensions</b> for order
   * (see {@link FilenameUtils#getExtension(String)}).
   * <p>
   * This comparator can be used to sort lists or arrays of files
   * by their file extension either in a case-sensitive, case-insensitive or
   * system dependant case sensitive way. A number of singleton instances
   * are provided for the various case sensitivity options (using {@link IOCase})
   * and the reverse of those options.
   * <p>
   * Example of a <i>case-sensitive</i> file extension sort using the
   * {@link #EXTENSION_COMPARATOR} singleton instance:
   * <pre>
   *       List&lt;File&gt; list = ...
   *       ExtensionFileComparator.EXTENSION_COMPARATOR.sort(list);
   * </pre>
   * <p>
   * Example of a <i>reverse case-insensitive</i> file extension sort using the
   * {@link #EXTENSION_INSENSITIVE_REVERSE} singleton instance:
   * <pre>
   *       File[] array = ...
   *       ExtensionFileComparator.EXTENSION_INSENSITIVE_REVERSE.sort(array);
   * </pre>
   * <p>
   *
   * @version $Revision: 1.1.2.1.2.1 $ $Date: 2011/01/15 20:32:24 $
   * @since Commons IO 1.4
   */
  public class ExtensionFileComparator extends AbstractFileComparator implements Serializable {
  
      /** Case-sensitive extension comparator instance (see {@link IOCase#SENSITIVE}) */
      public static final Comparator<File> EXTENSION_COMPARATOR = new ExtensionFileComparator();
  
      /** Reverse case-sensitive extension comparator instance (see {@link IOCase#SENSITIVE}) */
      public static final Comparator<File> EXTENSION_REVERSE = new ReverseComparator(EXTENSION_COMPARATOR);
  
      /** Case-insensitive extension comparator instance (see {@link IOCase#INSENSITIVE}) */
      public static final Comparator<File> EXTENSION_INSENSITIVE_COMPARATOR
                                                  = new ExtensionFileComparator(IOCase.INSENSITIVE);
  
      /** Reverse case-insensitive extension comparator instance (see {@link IOCase#INSENSITIVE}) */
      public static final Comparator<File> EXTENSION_INSENSITIVE_REVERSE
                                                  = new ReverseComparator(EXTENSION_INSENSITIVE_COMPARATOR);
  
      /** System sensitive extension comparator instance (see {@link IOCase#SYSTEM}) */
      public static final Comparator<File> EXTENSION_SYSTEM_COMPARATOR = new ExtensionFileComparator(IOCase.SYSTEM);
  
      /** Reverse system sensitive path comparator instance (see {@link IOCase#SYSTEM}) */
      public static final Comparator<File> EXTENSION_SYSTEM_REVERSE = new ReverseComparator(EXTENSION_SYSTEM_COMPARATOR);
  
      /** Whether the comparison is case sensitive. */
      private final IOCase caseSensitivity;
  
      /**
       * Construct a case sensitive file extension comparator instance.
       */
      public ExtensionFileComparator() {
          this.caseSensitivity = IOCase.SENSITIVE;
      }
  
      /**
       * Construct a file extension comparator instance with the specified case-sensitivity.
       *
       * @param caseSensitivity how to handle case sensitivity, null means case-sensitive
       */
      public ExtensionFileComparator(IOCase caseSensitivity) {
          this.caseSensitivity = caseSensitivity == null ? IOCase.SENSITIVE : caseSensitivity;
      }
  
      /**
       * Compare the extensions of two files the specified case sensitivity.
       * 
       * @param file1 The first file to compare
       * @param file2 The second file to compare
       * @return a negative value if the first file's extension
       * is less than the second, zero if the extensions are the
       * same and a positive value if the first files extension
       * is greater than the second file.
       * 
       */
      public int compare(File file1, File file2) {
          String suffix1 = FilenameUtils.getExtension(file1.getName());
          String suffix2 = FilenameUtils.getExtension(file2.getName());
          return caseSensitivity.checkCompareTo(suffix1, suffix2);
      }
  
      /**
       * String representation of this file comparator.
       *
       * @return String representation of this file comparator
       */
      @Override
      public String toString() {
          return super.toString() + "[caseSensitivity=" + caseSensitivity + "]";
      }
  }
  