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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 import java.io.Serializable;
     21 
     22 /**
     23  * This filter accepts files or directories that are empty.
     24  * <p>
     25  * If the <code>File</code> is a directory it checks that
     26  * it contains no files.
     27  * <p>
     28  * Example, showing how to print out a list of the
     29  * current directory's empty files/directories:
     30  *
     31  * <pre>
     32  * File dir = new File(".");
     33  * String[] files = dir.list( EmptyFileFilter.EMPTY );
     34  * for ( int i = 0; i &lt; files.length; i++ ) {
     35  *     System.out.println(files[i]);
     36  * }
     37  * </pre>
     38  *
     39  * <p>
     40  * Example, showing how to print out a list of the
     41  * current directory's non-empty files/directories:
     42  *
     43  * <pre>
     44  * File dir = new File(".");
     45  * String[] files = dir.list( EmptyFileFilter.NOT_EMPTY );
     46  * for ( int i = 0; i &lt; files.length; i++ ) {
     47  *     System.out.println(files[i]);
     48  * }
     49  * </pre>
     50  *
     51  * @since Commons IO 1.3
     52  * @version $Revision: 587916 $
     53  */
     54 public class EmptyFileFilter extends AbstractFileFilter implements Serializable {
     55 
     56     /** Singleton instance of <i>empty</i> filter */
     57     public static final IOFileFilter EMPTY = new EmptyFileFilter();
     58 
     59     /** Singleton instance of <i>not-empty</i> filter */
     60     public static final IOFileFilter NOT_EMPTY = new NotFileFilter(EMPTY);
     61 
     62     /**
     63      * Restrictive consructor.
     64      */
     65     protected EmptyFileFilter() {
     66     }
     67 
     68     /**
     69      * Checks to see if the file is empty.
     70      *
     71      * @param file  the file or directory to check
     72      * @return <code>true</code> if the file or directory
     73      *  is <i>empty</i>, otherwise <code>false</code>.
     74      */
     75     public boolean accept(File file) {
     76         if (file.isDirectory()) {
     77             File[] files = file.listFiles();
     78             return (files == null || files.length == 0);
     79         } else {
     80             return (file.length() == 0);
     81         }
     82     }
     83 
     84 }
     85