Varargs in Java HashMap

Question

HashMap <String,String... strings> hm = new HashMap<String,String... strings>();

hm.put("Zara", "Pony","Cars", "Magic");
hm.put("John", "Horse","Flying", "Loving");

How can I do that? It's not letting me.

You can't. You'll need to use a Map<String, String[]> instead. — BackSlash
– BackSlash, Commented Mar 29, 2018 at 7:08
Varargs are only for function arguments. What do you actually want in the values of the map? — Mad Physicist
– Mad Physicist, Commented Mar 29, 2018 at 7:09
@ScaryWombat I recently did 4 question graduate position test, in which I got 0% correct. And one of the questions had something like this in the test. — calimses
– calimses, Commented Mar 29, 2018 at 7:33

Mureinik · Accepted Answer · 2018-03-29 07:12:50Z

5

The elipsis (...) operator can only be used in method signatures. You could explicitly declare and create arrays:

Map<String, String[]> hm = new HashMap<>();

hm.put("Zara", new String[]{"Pony", "Cars", "Magic"});
hm.put("John", new String[]{"Horse", "Flying", "Loving"});

If you absolutely must use varags, you can wrap the call to Map#put with your own method:

public static void main(String[] args) {
    Map<String, String[]> hm = new HashMap<>();

    addToMap(hm, "Zara", "Pony", "Cars", "Magic");
    addToMap(hm, "John", "Horse", "Flying", "Loving");
}

private static void addToMap
    (Map<String, String[]> map, String key, String... values) {
    map.put(key, values);
}

answered Mar 29, 2018 at 7:12

Mureinik

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Mad Physicist · Accepted Answer · 2018-03-29 13:18:22Z

3

Vararg notation is only for use with functions that allow it. It can not be used anywhere else.

You have to decide what you actually want your map values to be. Normally varargs is basically syntactic sugar for an array. However, a List or Set also makes sense here.

Either of the following would work:

Array:

HashMap <String, String[]> hm = new HashMap<>();
hm.put("Zara", new String[] {"Pony","Cars", "Magic"});
hm.put("John", new String[] {"Horse", "Flying", "Loving"});

List:

HashMap <String, List<String>> hm = new HashMap<>();
hm.put("Zara", new ArrayList<String>());
hm.get("Zara").add("Pony");
hm.get("Zara").add("Cars");
hm.get("Zara").add("Magic");
hm.put("John", new ArrayList<String>());
hm.get("John").add("Horse");
hm.get("John").add("Flying");
hm.get("John").add("Loving");

edited Mar 29, 2018 at 13:18

answered Mar 29, 2018 at 7:16

Mad Physicist

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Comments

daniu · Accepted Answer · 2018-03-29 07:11:46Z

1

Closest you can do is use a `Map and create a method for that

public static void addToMap(Map<String, String[]> map, String key, String...values) {
    map.put(key, values);
}

answered Mar 29, 2018 at 7:11

daniu

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Yassine Badache · Accepted Answer · 2018-03-29 07:12:11Z

0

See this question. Basically you need to do the following:

hm.put("Zara", new String[]{"Pony", "Cars", "Magic"});

Or if you want to declare it separetely:

String[] zaraValues = new String[]{"Pony", "Cars", "Magic"};
hm.put("Zara", zaraValues);

answered Mar 29, 2018 at 7:12

Yassine Badache

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Andreas · Accepted Answer · 2018-03-29 07:14:22Z

0

You might be looking for this:

HashMap<String, List<String>> hm = new HashMap<>();
hm.put("Zara", Arrays.asList("Pony", "Cars", "Magic"));
hm.put("John", Arrays.asList("Horse", "Flying", "Loving"));

answered Mar 29, 2018 at 7:14

Andreas

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