Clojure :: (String/format "%s" "a") :: fails with ClassCastException

Question

The following call:

(String/format "%s" "a")

... throws a "ClassCastException java.lang.String cannot be cast to [Ljava.lang.Object" exception in Clojure.

(String/format "%s" (cast Object "a"))

.... produces the same exception.

Any reason you need to use String.format and not Clojure.core/format - it wraps with to-array for you? (format "%s" "a") — Kyle
– Kyle, Commented Jan 14, 2013 at 16:55
No reason to use String.format in particular, just being curious ... — Marcus Junius Brutus
– Marcus Junius Brutus, Commented Jan 14, 2013 at 17:09

mishadoff · Accepted Answer · 2013-01-14 17:00:16Z

14

Because last argument in java API is array Object[] instead of Object.

Just call (String/format "%s" (into-array ["a"]))

But more idiomatic to use (format "Hello %s" "world")

answered Jan 14, 2013 at 17:00

mishadoff

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iced · Accepted Answer · 2013-01-14 16:53:50Z

4

[L means "I want array" so use (String/format "%s" (to-array "a")). General syntax: (to-array ["a" 42 0.666]).

answered Jan 14, 2013 at 16:53

iced

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skuro · Accepted Answer · 2013-01-14 16:55:25Z

4

String.format is using varargs, which are internally plain Java arrays. You then need to convert the input parameters into an array, e.g. by using to-array:

user=> (String/format "%s" (to-array "a"))
"a"

answered Jan 14, 2013 at 16:55

skuro

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