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The Apache Commons IO library contains utility classes, stream implementations, file filters, file comparators, endian transformation classes, and much more.

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/*
 * 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;

/**
 * Compare two files using the {@link File#isDirectory()} method.
 * 
 * This comparator can be used to sort lists or arrays by directories and files.
 * 

 * Example of sorting a list of files/directories using the
 * {@link #DIRECTORY_COMPARATOR} singleton instance:
 * 
 *       List<File> list = ...
 *       ((AbstractFileComparator) DirectoryFileComparator.DIRECTORY_COMPARATOR).sort(list);
 * 
 * 
 * Example of doing a reverse sort of an array of files/directories using the
 * {@link #DIRECTORY_REVERSE} singleton instance:
 * 
 *       File[] array = ...
 *       ((AbstractFileComparator) DirectoryFileComparator.DIRECTORY_REVERSE).sort(array);
 * 
 * 
 *
 * @version $Id: DirectoryFileComparator.java 1642757 2014-12-01 21:09:30Z sebb $
 * @since 2.0
 */
public class DirectoryFileComparator extends AbstractFileComparator implements Serializable {

    private static final long serialVersionUID = 296132640160964395L;

    /** Singleton default comparator instance */
    public static final Comparator DIRECTORY_COMPARATOR = new DirectoryFileComparator();

    /** Singleton reverse default comparator instance */
    public static final Comparator DIRECTORY_REVERSE = new ReverseComparator(DIRECTORY_COMPARATOR);

    /**
     * Compare the two files using the {@link File#isDirectory()} method.
     * 
     * @param file1 The first file to compare
     * @param file2 The second file to compare
     * @return the result of calling file1's
     * {@link File#compareTo(File)} with file2 as the parameter.
     */
    public int compare(final File file1, final File file2) {
        return getType(file1) - getType(file2);
    }

    /**
     * Convert type to numeric value.
     *
     * @param file The file
     * @return 1 for directories and 2 for files
     */
    private int getType(final File file) {
        if (file.isDirectory()) {
            return 1;
        } else {
            return 2;
        }
    }
}