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Asked: 2026-05-27T17:56:33+00:00

I am running Clojure 1.3.0 with La Clojure in IntelliJ IDEA while reading The

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I am running Clojure 1.3.0 with La Clojure in IntelliJ IDEA while reading The Joy Of Clojure, and on section 4.1.3 (page 64), the authors demonstrate integer overflow with the following code:

(+ Integer/MAX_VALUE Integer/MAX_VALUE)
;=> java.lang.ArithmeticException: integer overflow

However, when I try it out on the REPL, I get instead

user=> (+ Integer/MAX_VALUE Integer/MAX_VALUE)
4294967294

user=> Integer/MAX_VALUE
2147483647

What is happening here? Why are my integers being added correctly instead of overflowing?

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1 Answer

  1. Editorial Team

    (edited) Clojure (at least 1.3.0) automatically converts the integer to a long if necessary. For more details about automatic boxing, promotion and primitive numeric type support in Clojure 1.3.0 check the Documentation for Clojure 1.3.0 Numerics.

    The reason you don’t get an overflow is because Clojure automatically converts the integer to a long, so (+ Integer/MAX_VALUE Integer/MAX_VALUE) is adding two longs:

    user> (type Integer/MAX_VALUE)
java.lang.Long
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