DirectoryFileComparator.java

/*
 * 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.
 * <p>
 * This comparator can be used to sort lists or arrays by directories and files.
 * </p>
 * <p>
 * Example of sorting a list of files/directories using the {@link #DIRECTORY_COMPARATOR} singleton instance:
 * </p>
 *
 * <pre>
 *       List&lt;File&gt; list = ...
 *       ((AbstractFileComparator) DirectoryFileComparator.DIRECTORY_COMPARATOR).sort(list);
 * </pre>
 * <p>
 * Example of doing a <em>reverse</em> sort of an array of files/directories using the {@link #DIRECTORY_REVERSE}
 * singleton instance:
 * </p>
 *
 * <pre>
 *       File[] array = ...
 *       ((AbstractFileComparator) DirectoryFileComparator.DIRECTORY_REVERSE).sort(array);
 * </pre>
 * <h2>Deprecating Serialization</h2>
 * <p>
 * <em>Serialization is deprecated and will be removed in 3.0.</em>
 * </p>
 *
 * @since 2.0
 */
public class DirectoryFileComparator extends AbstractFileComparator implements Serializable {

    private static final int TYPE_FILE = 2;

    private static final int TYPE_DIRECTORY = 1;

    private static final long serialVersionUID = 296132640160964395L;

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

    /** Singleton reverse default comparator instance */
    public static final Comparator<File> DIRECTORY_REVERSE = new ReverseFileComparator(DIRECTORY_COMPARATOR);

    /**
     * Construct a new instance.
     */
    public DirectoryFileComparator() {
        // empty
    }

    /**
     * Compares 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.
     */
    @Override
    public int compare(final File file1, final File file2) {
        return getType(file1) - getType(file2);
    }

    /**
     * Converts type to numeric value.
     *
     * @param file The file.
     * @return 1 for directories and 2 for files.
     */
    private int getType(final File file) {
        return file.isDirectory() ? TYPE_DIRECTORY : TYPE_FILE;
    }
}