Why Is String Formatting Causing a Casting Exception?

Question

Why does (String/format "%8s" (Integer/toBinaryString 6)) result in a java.lang.ClassCastException: java.lang.String cannot be cast to [Ljava.lang.Object casting exception?

Jon Skeet · Accepted Answer · 2011-10-04 04:09:22Z

8

I don't know Clojure, but I suspect that's trying to call the method as if it were the Java:

String.format("%8s", Integer.toBinaryString(6));

but without the varargs support. I suspect you want:

(String/format "%8s" (into-array Object (Integer/toBinaryString 6)))

See this mailing list thread for more information from people who actually do know Clojure :)

answered Oct 4, 2011 at 4:09

Jon Skeet

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2 Comments

amalloy Over a year ago

Yes, this is exactly the issue. A better solution than using String/format and into-array is to just use the Clojure function format, which takes varargs Clojure-style and otherwise behaves the same as String/format.

Jon Skeet Over a year ago

@amalloy: Indeed, as noted on the mailing list thread. I didn't want to get too far off the track of what I thought I'd be able to get away with in terms of correct code :)

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