(Kotlin was used as the first level development language of Android in 2017 and was established as the preferred development language of Android in 2019. In recent years, the development of the language has received unprecedented support and attention. Kotlin language is also favored in the back-end development posts of some large factories. More and more back-end Posts put forward new requirements and standards for the mastery of kotlin language. This course is based on kotlin1 Version 3. X takes you to build kotlin knowledge system. To meet the current market demand, increasing the job search weight is a good choice for Android development and back-end development engineers.)