자바 강좌
https://opentutorials.org/course/1223
안드로이드 코틀린 강좌
https://www.youtube.com/watch?v=LbQEpdqW354&list=PLSBIrFmNg2Jba38lQe9sozHa-4gUMU7lO
안드로이드 강좌
http://bcho.tistory.com/1036?category=584380
https://kairo96.gitbooks.io/android/content/ch0.html
http://basicto.tistory.com/638
https://developer.android.com/guide/topics/text/creating-input-method
안드로이드 소프트키보드 강좌
https://mcauto.github.io/android/2018/01/29/make-android-custom-keyboard/
https://stackoverflow.com/questions/9577304/how-to-make-an-android-custom-keyboard
https://www.androidauthority.com/lets-build-custom-keyboard-android-832362/
https://code.tutsplus.com/tutorials/create-a-custom-keyboard-on-android--cms-22615
https://github.com/tutsplus/Android-CustomKeyboard
샘플
http://www.java2s.com/Open-Source/Android_Free_Code/Development/keyboard/index.htm