[코틀린] 데이터베이스 헬퍼

class DatabaseHelper(context: Context) : SQLiteOpenHelper(context, "notepad_kot.db", null, 1) {

    override fun onCreate(db: SQLiteDatabase?) {
        val sql = ("create table if not exists noteData(" +
                "_id integer PRIMARY KEY autoincrement," +
                "title text," +
                "content text," +
                "time text)")

        // !!는 null이 아님을 명시
        db!!.execSQL(sql)
    }

    override fun onUpgrade(db: SQLiteDatabase?, oldVersion: Int, newVersion: Int) {
        if (newVersion > oldVersion) {
            db!!.execSQL("DROP TABLE IF EXISTS noteData")
        }
    }
}