Convert an entrySet to an array

Question

I'd like to convert the entrySet() of an Map<String, Statistic> to an array (or ArrayList).

I tried:

Map.Entry<String, Statistic>[] entries = statisticMap.entrySet().toArray(new Map.Entry<String, Statistic>[0]);

but this gives the compiler error: "Cannot create a generic array of Map.Entry"

Even this does not work, with same error:

Map.Entry<String, Statistic>[] entries = new Map.Entry<String, Statistic>[1];

But this works:

Map.Entry[] entries = new Map.Entry[1];

Any ideas how to create such a array or list?

possible duplicate of [How do you instantiate a Map.Entry array in Java?](http://stackoverflow.com/questions/8504045/how-do-you-instantiate-a-map-entryk-v-array-in-java) — Eran, Jul 24 '14 at 20:29
The above anwer in the duplicate is less suitable than Peters answer below. — AlexWien, Jul 24 '14 at 20:45

score 5 · Answer 1 · answered Jul 27 '14 at 03:32

If you're willing to get a list instead of an array, you can do this:

List<Map.Entry<String, Statistic>> list = new ArrayList<>(map.entrySet());

Using a list avoids the problems creating arrays of generics, and it also lets you use the "diamond operator" of Java 7 to avoid repeating the type arguments.

score 2 · Accepted Answer · answered Jul 24 '14 at 20:28

2

Any ideas how to create such a array or list?

You can do this, though it is ugly.

Map.Entry<String, Statistic>[] entries = 
                          (Map.Entry<String, Statistic>[]) new Map.Entry[num];

answered Jul 24 '14 at 20:28

Peter Lawrey

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Yes its ugly, and it shows that there is a better solution in my App using a SortedMap – AlexWien Jul 24 '14 at 20:50

score -1 · Answer 3 · answered Mar 11 '20 at 06:48

Well, the root reason for complication is the broken Java design, compared to C#, where Array and List doesn't implement the same interface. So, any solution will be ugly (and with performance penalty).

If going ugly, personally I prefer explicit solutions, where at least you can see whats actually going on.

Therefore, my ugly version is:

Map.Entry<String, String>[] keys = new Map.Entry[map.entrySet().size()];

int index = 0;
for (Map.Entry<String, String> entry: map.entrySet()) {

     keys[index] = entry;
     index++;
}

Convert an entrySet to an array

3 Answers3