If you read the book alone, it was very helpful to review the knowledge that you might have missed and the knowledge that you vaguely knew. Going further, if you study in depth, you are provided with good knowledge, and you can proceed while referring to this. There are many parts where the contents that came before are linked to the items that come after, so the more you read, the easier it is to read the later parts, and the magic unfolds. The content that I learned here is Java in-depth knowledge that becomes flesh and blood when using Kotlin, so I think it is better because you can use it in conjunction. Thank you for providing a great lecture!