Once upon a time, there were Crab Apples. They were extremely sour (except perhaps for the Chestnut Crabapple) and contained a lot of Pectin, a soluble fibre/fiber. Then, we clever humans selectively bred apple trees over a large number of years and voila! We have the modern-day apple. Note that this contains on average 10.4g of sugar/100g of apple and only 2.4g of fibre/100g of apple. The British Dental Association claims that the Pink Lady, Braeburn and Fuji contain so much sugar that they cause tooth decay.
Different types of fruit vary hugely in their sugar content. Some fruits (blueberries & cranberries) also contain mannose. Bananas also contain starch, which turns into sugars as the banana changes colour from green to yellow to black.
Don't eat/drink too much fructose, as that goes straight to your liver where it tops-up liver glycogen and, once your liver glycogen stores are full, overspills as triglycerides a.k.a. fats into your liver & blood.
For more on fructose, see Sugar: The Bitter Truth by Robert H. Lustig, M.D.
As glucose and fructose have very different effects on the body, this is a situation where "a calorie isn't a calorie".