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1   /*
2    * Licensed to the Apache Software Foundation (ASF) under one or more
3    * contributor license agreements.  See the NOTICE file distributed with
4    * this work for additional information regarding copyright ownership.
5    * The ASF licenses this file to You under the Apache License, Version 2.0
6    * (the "License"); you may not use this file except in compliance with
7    * the License.  You may obtain a copy of the License at
8    * 
9    *      http://www.apache.org/licenses/LICENSE-2.0
10   * 
11   * Unless required by applicable law or agreed to in writing, software
12   * distributed under the License is distributed on an "AS IS" BASIS,
13   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14   * See the License for the specific language governing permissions and
15   * limitations under the License.
16   */
17  package org.apache.commons.io.filefilter;
18  
19  import java.io.File;
20  
21  /**
22   * This filter accepts files or directories that are empty.
23   * <p>
24   * If the <code>File</code> is a directory it checks that
25   * it contains no files.
26   * <p>
27   * Example, showing how to print out a list of the 
28   * current directory's empty files/directories:
29   *
30   * <pre>
31   * File dir = new File(".");
32   * String[] files = dir.list( EmptyFileFilter.EMPTY );
33   * for ( int i = 0; i &lt; files.length; i++ ) {
34   *     System.out.println(files[i]);
35   * }
36   * </pre>
37   *
38   * <p>
39   * Example, showing how to print out a list of the 
40   * current directory's non-empty files/directories:
41   *
42   * <pre>
43   * File dir = new File(".");
44   * String[] files = dir.list( EmptyFileFilter.NOT_EMPTY );
45   * for ( int i = 0; i &lt; files.length; i++ ) {
46   *     System.out.println(files[i]);
47   * }
48   * </pre>
49   *
50   * @since Commons IO 1.3
51   * @version $Revision: 437567 $
52   */
53  public class EmptyFileFilter extends AbstractFileFilter {
54      
55      /** Singleton instance of <i>empty</i> filter */
56      public static final IOFileFilter EMPTY = new EmptyFileFilter();
57      
58      /** Singleton instance of <i>not-empty</i> filter */
59      public static final IOFileFilter NOT_EMPTY = new NotFileFilter(EMPTY);
60      
61      /**
62       * Restrictive consructor.
63       */
64      protected EmptyFileFilter() {
65      }
66      
67      /**
68       * Checks to see if the file is empty.
69       * 
70       * @param file  the file or directory to check
71       * @return <code>true</code> if the file or directory
72       *  is <i>empty</i>, otherwise <code>false</code>.
73       */
74      public boolean accept(File file) {
75          if (file.isDirectory()) {
76              File[] files = file.listFiles();
77              return (files == null || files.length == 0);
78          } else {
79              return (file.length() == 0);
80          }
81      }
82      
83  }