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Editorial Team
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Asked: 2026-05-22T03:19:31+00:00

The following code throws an ArrayStoreException at toArray() . Should not the compiler have

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The following code throws an ArrayStoreException at toArray(). Should not the compiler have caught the blunder and reported an type conflict given that toArray takes a V[] and the registry Map is typed with a value of Map<String,String>?

private Map<String,Map<String,String>>  registry;

...

registry=new TreeMap<String,Map<String,String>>(String.CASE_INSENSITIVE_ORDER));

...

void removeTargets(String[] clsarr, String hdl) {
        if(clsarr==null) { clsarr=registry.values().toArray(new String[0]); }
    ...
    }

It looks like a compiler bug to me.

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1 Answer

  1. Editorial Team

    Not a compiler bug. Arguably a library bug though.

    The type of Collection.toArray() is <T> T[] toArray(T[] a). Note that T is a type parameter to the toArray method and has no relationship to Collection‘s type parameter.

    This bug would have been caught if the signature of Collection.toArray were <T super E> T[] toArray(T[] a) but that would make it tough to use since it’s not legal to do new Map<String, String>[0] — you get a “generic array creation” error.

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