How to convert Map<String, Set<String>> to Map<String, String[]> in Java

Question

I am getting data in the form of Map<String, Set<String>> from a method. But I want it to be in the form of Map<String, String[]>.

I.e, i want to convert only map values from Set<String> to String[] array for a particular key.

I tried this way , iterating the loaded set map and getting the String[] array of values correctly for a key.

But I just want to know that, is there any better solution than this.

Map<String, Set<String>> testmap = new HashMap<String, Set<String>>();
        Map<String, String[]> testmapArray = new HashMap<String, String[]>();
        Set<String> testSet = new TreeSet<String>();
        testSet.add("1");
        testSet.add("2");
        testSet.add("3");

        testmap.put("A", testSet);
        testmapArray.put("A", testSet.toArray(new String[testSet.size()]));

        Set<String> testSet1 = new TreeSet<String>();
        testSet1.add("4");
        testSet1.add("5");
        testSet1.add("6");

        testmap.put("B", testSet1);
        testmapArray.put("A", testSet1.toArray(new String[testSet1.size()]));

        System.out.println(testmap);

        Iterator it = testmap.entrySet().iterator();
        while (it.hasNext()) {
            Map.Entry pair = (Map.Entry)it.next();
            testmapArray.put(pair.getKey().toString(), testmap.get(pair.getKey()).toArray(new String[testmap.get(pair.getKey()).size()]));
        }
        System.out.println(testmapArray);

Can anyone help me?

@Tom yes.. that is the reason i posted this as, I am getting some warnings out of this code..!!! — user1660325
– user1660325, Commented Aug 24, 2015 at 9:11
So? Since you already know what generic types are (you already using them), you should be able to not use a raw Iterator. So add the generic types. You can do that :). — Tom
– Tom, Commented Aug 24, 2015 at 9:12

Dmitry Ginzburg · Accepted Answer · 2015-08-24 09:12:32Z

3

Your solution is nearly working, so you should just consider couple of things:

Iterator is generic type, so you shouldn't do additional casting
There's no point in using Iterator explicitly: for loop is doing that implicitly for every Iterable (which Collection -> Set is)
You're using only key in Map.Entry, but you can use value too, there's no need to call get two additional times

So, the conversion would be:

for (Map.Entry<String, Set<String>> entry: testmap.entrySet()) {
    testmapArray.put(entry.getKey(),
            entry.getValue().toArray(new String[entry.getValue().size()]));
}

answered Aug 24, 2015 at 9:12

Dmitry Ginzburg

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Comments

akhil_mittal · Accepted Answer · 2015-08-24 09:45:10Z

0

In case you are using Java 8 then you can achieve it using streams:

testmapArray = testmap.entrySet().stream().collect(Collectors.toMap(entry ->  entry.getKey(), entry-> setToArray(entry.getValue())));

The method setToArray is:

private static String[] setToArray(Set<String> set) {
        return set.toArray(new String[set.size()]);
    }

answered Aug 24, 2015 at 9:45

akhil_mittal

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