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Collections are a way for you to organize kata so that you can create your own training routines. Every collection you create is public and automatically sharable with other warriors. After you have added a few kata to a collection you and others can train on the kata contained within the collection.
Get started now by creating a new collection.
s.charAt() will returns character type data so when you concate with "", it will become String type
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(one of the trickiest too, actually....! x) )
Yup, it's one of the most powerful feature in programming. You won't regret learning it :)