001/*
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements.  See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License.  You may obtain a copy of the License at
008 *
009 *      http://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 */
017package org.apache.commons.io.filefilter;
018
019import java.io.File;
020import java.io.Serializable;
021
022/**
023 * This filter accepts files or directories that are empty.
024 * <p>
025 * If the <code>File</code> is a directory it checks that
026 * it contains no files.
027 * <p>
028 * Example, showing how to print out a list of the
029 * current directory's empty files/directories:
030 *
031 * <pre>
032 * File dir = new File(".");
033 * String[] files = dir.list( EmptyFileFilter.EMPTY );
034 * for ( int i = 0; i &lt; files.length; i++ ) {
035 *     System.out.println(files[i]);
036 * }
037 * </pre>
038 *
039 * <p>
040 * Example, showing how to print out a list of the
041 * current directory's non-empty files/directories:
042 *
043 * <pre>
044 * File dir = new File(".");
045 * String[] files = dir.list( EmptyFileFilter.NOT_EMPTY );
046 * for ( int i = 0; i &lt; files.length; i++ ) {
047 *     System.out.println(files[i]);
048 * }
049 * </pre>
050 *
051 * @since 1.3
052 *
053 */
054public class EmptyFileFilter extends AbstractFileFilter implements Serializable {
055
056    private static final long serialVersionUID = 3631422087512832211L;
057
058    /** Singleton instance of <i>empty</i> filter */
059    public static final IOFileFilter EMPTY = new EmptyFileFilter();
060
061    /** Singleton instance of <i>not-empty</i> filter */
062    public static final IOFileFilter NOT_EMPTY = new NotFileFilter(EMPTY);
063
064    /**
065     * Restrictive constructor.
066     */
067    protected EmptyFileFilter() {
068    }
069
070    /**
071     * Checks to see if the file is empty.
072     *
073     * @param file  the file or directory to check
074     * @return {@code true} if the file or directory
075     *  is <i>empty</i>, otherwise {@code false}.
076     */
077    @Override
078    public boolean accept(final File file) {
079        if (file.isDirectory()) {
080            final File[] files = file.listFiles();
081            return files == null || files.length == 0;
082        }
083        return file.length() == 0;
084    }
085
086}