I need to input a number using read-line:
(def x (read-line))
user => 1
gives the error:
CompilerException java.lang.ClassCastException: java.lang.String cannot be cast to java.lang.Number
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1 Answer
That code alone won't cause that error.
read-line returns a String, and I'm guessing you're trying to use x in the context where a number is expected.
To reproduce the error, you could do:
(def x (read-line)) ; Enter 1
(+ 1 x) ; Same as (+ 1 "1"), which should make the problem obvious
ClassCastException java.lang.String cannot be cast to java.lang.Number clojure.lang.Numbers.add (Numbers.java:128)
Change it to use Long/parseLong (or a similar function):
(def x (Long/parseLong (read-line)))
You need to parse x as a number (Long in this case) before it can be used as a number.
(def x (Long/parseLong (read-line)))
(+ 1 x)
=> 2
Of course though, Long/parseLong will throw if you try to have it parse something that can't be represented as a number. In the real world, you'll want to do proper error handling via try.
