How to check for key in a Map irrespective of the case? [duplicate]

Question

I want to know whether a particular key is present in a HashMap, so i am using containsKey(key) method. But it is case sensitive ie it does not returns true if there is a key with Name and i am searching for name. So is there any way i can know without bothering the case of the key?

thanks

Answer 1

Not with conventional maps.

"abc" is a distinct string from "ABC", their hashcodes are different and their equals() methods will return false with respect to each other.

The simplest solution is to simply convert all inputs to uppercase (or lowercase) before inserting/checking. You could even write your own Map wrapper that would do this to ensure consistency.

If you want to maintain the case of the key as provided, but with case-insensitive comparison, you could look into using a TreeMap and supplying your own Comparator that will compare case-insensitively. However, think hard before going down this route as you will end up with some irreconcilable inconsistencies - if someone calls map.put("abc", 1) then map.put("ABC", 2), what case is the key stored in the map? Can you even make this make sense? Are you comfortable with the fact that if someone wraps your map in a standard e.g. HashMap you'll lose functionality? Or that if someone happens to be iterating through your keyset anyway, and does their own quick "contains" check by using equals() you'll get inconsistent results? There will be lots of other cases like this too. Note that you're violating the contract of Map by doing this (as key equality is defined in terms of the equals() method on the keys) so it's really not workable in any sense.

Maintaining a strict uppercase map is much easier to work with and maintain, and has the advantage of actually being a legal Map implementation.