为什么文件占用空间跟文件大小不一样

/**
     * 常规文件可能会有很多不必要的空间浪费
     * @throws IOException
     */
    @Test
    public void normalFile() throws IOException {
        File file = new File("d:/tmp/sparse.txt");
        Path path = file.toPath();
        FileChannel ch = FileChannel.open(path, StandardOpenOption.CREATE,StandardOpenOption.WRITE);
        ch.position(5*1024*1024L);
        ch.write(ByteBuffer.wrap("hello world".getBytes("utf-8")));
        ch.close();

    }

    /**
     * 稀疏文件模式
     * @throws IOException
     */
    @Test
    public void sparseFile() throws IOException {
        File file = new File("d:/tmp/sparse.txt");
        Path path = file.toPath();
        FileChannel ch = FileChannel.open(path, StandardOpenOption.SPARSE,StandardOpenOption.CREATE_NEW,StandardOpenOption.WRITE);
        ch.position(5*1024*1024L);
        ch.write(ByteBuffer.wrap("hello world".getBytes("utf-8")));
        ch.close();
    }