Commons IO example source code file (CompositeFileComparator.java)

This example Commons IO source code file (CompositeFileComparator.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Java - Commons IO tags/keywords

comparator, comparator, compositefilecomparator, compositefilecomparator, file, io, no_comparators, no_comparators, ok, override, serializable, string, stringbuilder, stringbuilder, suppresswarnings, util

The Commons IO CompositeFileComparator.java source code

/*
 * 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.ArrayList;
import java.util.Comparator;
import java.util.List;

/**
 * Compare two files using a set of delegate file {@link Comparator}.
 * <p>
 * This comparator can be used to sort lists or arrays of files
 * by combining a number other comparators.
 * <p>
 * Example of sorting a list of files by type (i.e. directory or file)
 * and then by name:
 * <pre>
 *       CompositeFileComparator comparator =
 *                       new CompositeFileComparator(
 *                                   DirectoryFileComparator.DIRECTORY_COMPARATOR,
 *                                   NameFileComparator.NAME_COMPARATOR);
 *       List<File> list = ...
 *       comparator.sort(list);
 * </pre>
 *
 * @version $Revision: 896991 $ $Date: 2010-01-07 20:03:42 +0000 (Thu, 07 Jan 2010) $
 * @since Commons IO 2.0
 */
public class CompositeFileComparator extends AbstractFileComparator implements Serializable {

    private static final Comparator<?>[] NO_COMPARATORS = {};
    private final Comparator<File>[] delegates;

    /**
     * Create a composite comparator for the set of delegate comparators.
     *
     * @param delegates The delegate file comparators
     */
    @SuppressWarnings("unchecked") // casts 1 & 2 must be OK because types are already correct
    public CompositeFileComparator(Comparator<File>... delegates) {
        if (delegates == null) {
            this.delegates = (Comparator<File>[]) NO_COMPARATORS;//1
        } else {
            this.delegates = (Comparator<File>[]) new Comparator[delegates.length];//2
            System.arraycopy(delegates, 0, this.delegates, 0, delegates.length);
        }
    }

    /**
     * Create a composite comparator for the set of delegate comparators.
     *
     * @param delegates The delegate file comparators
     */
    @SuppressWarnings("unchecked") // casts 1 & 2 must be OK because types are already correct
    public CompositeFileComparator(Iterable<Comparator delegates) {
        if (delegates == null) {
            this.delegates = (Comparator<File>[]) NO_COMPARATORS; //1
        } else {
            List<Comparator list = new ArrayList>();
            for (Comparator<File> comparator : delegates) {
                list.add(comparator);
            }
            this.delegates = (Comparator<File>[]) list.toArray(new Comparator[list.size()]); //2
        }
    }

    /**
     * Compare the two files using delegate comparators.
     * 
     * @param file1 The first file to compare
     * @param file2 The second file to compare
     * @return the first non-zero result returned from
     * the delegate comparators or zero.
     */
    public int compare(File file1, File file2) {
        int result = 0;
        for (Comparator<File> delegate : delegates) {
            result = delegate.compare(file1, file2);
            if (result != 0) {
                break;
            }
        }
        return result;
    }

    /**
     * String representation of this file comparator.
     *
     * @return String representation of this file comparator
     */
    @Override
    public String toString() {
        StringBuilder builder = new StringBuilder();
        builder.append(super.toString());
        builder.append('{');
        for (int i = 0; i < delegates.length; i++) {
            if (i > 0) {
                builder.append(',');
            }
            builder.append(delegates[i]);
        }
        builder.append('}');
        return builder.toString();
    }
}