/*
DirWriterに探索までさせているのは
DirWriterにファイルへの出力だけを任せるのなら
別に新たなクラスを作ることなくたとえばFileWriter等に任せれば事足りるから
DirListが窓口でDirWriterが実際の仕事というように分けてみた
*/
 
import java.io.*;
import java.util.*;
 
public class DirList {
    public static void main(String[] args) throws FileNotFoundException {
        Scanner sc = new Scanner(System.in);
        System.out.print("一覧を生成するディレクトリ名: ");
        String dir = sc.nextLine();
        System.out.print("出力ファイル名: ");
        String out = sc.nextLine();
        try (DirWriter dw = new DirWriter(out)) {
            dw.list(dir);
        }
        sc.close();
    }
}
 
class DirWriter implements AutoCloseable {
    private PrintWriter writer;
 
    public DirWriter(String fileName) throws FileNotFoundException {
        writer = new PrintWriter(fileName);
    }
 
    public void close() {
        writer.close();
    }
 
    public void list(String fileName) throws FileNotFoundException {
        File f = new File(fileName);
        if (f.isDirectory()) {
            list(f);
        } else if (f.exists()) {
            writer.println(fileName);
        } else {
            throw new FileNotFoundException(fileName);
        }
    }
 
    private void list(File dir) {
        Queue<File> que = new LinkedList<>();
        que.add(dir);
        while (! que.isEmpty()) {
            dir = que.remove();
            writer.println("Directory: " + dir.getName());
            File[] dirlist = dir.listFiles();
            Arrays.sort(dirlist, new Comparator<File>() {
                public int compare(File o1, File o2) {
                    return o1.getName().compareToIgnoreCase(o2.getName());
                }
            });
            for (File f : dirlist) {
                writer.print(f.getName());
                if (f.isDirectory()) {
                    writer.print(" はディレクトリです。");
                    que.add(f);
                }
                writer.println();
            }
        }
    }
}
 

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