为啥 Java 写入十六进制的文件，内容一直以 0a 结尾呢？

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    @Test
    public void testWrite() throws IOException {
        File file = new File("/home/my.test");
        file.createNewFile();
        int b = 0x1B, a = 0x78, c = 0x6f, d = 0x3f;
        FileOutputStream fos = new FileOutputStream(file);
        fos.write(a);
        fos.write(b);
        fos.write(c);
        fos.write(d);
        fos.close();
    }

nothing 如图和代码，我只是想写入四个十六进制的数值进去，并且在 vim 下用%!xxd 下能看到的十六进制的数值只有 4 个。但实际上我看到的却有五个，多了一个0a，这是啥特殊情况呢？求教！