Fast way to load all alphabetic characters to a hashmap

Question

For example I have this Hashmap:

Map<String,Integer> map = new HashMap<>();

Instead of doing map.put("A",0), map.put("B",0)... until map.put("C",0), is there any way we can make it fast?

Is this a simplified example? If not, why would you want to do this? Else use an array with indexing convention [char - 'A'] — Bathsheba, Feb 25 '14 at 09:35

score 26 · Accepted Answer · answered Feb 25 '14 at 09:35

26

Do it in for loop:

for (char ch = 'A'; ch <= 'Z'; ++ch) 
  map.put(String.valueOf(ch), 0);

answered Feb 25 '14 at 09:35

Dmitry Bychenko

180,369
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rai.skumar · Answer 2 · 2014-02-26T05:21:41.267

5

Use double brace initialization. It's very compact and helpful in initializing collections.

Map<String, Integer> map = new HashMap<String, Integer>() {
        {
            for (char ch = 'A'; ch <= 'Z'; ++ch) 
                put(String.valueOf(ch), 0); 
        }
};

Note that - put method is called without the map reference.

edited Feb 26 '14 at 05:21

answered Feb 25 '14 at 10:32

rai.skumar

10,309
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score 1 · Answer 3 · answered Feb 25 '14 at 09:39

1

Try this:

Map<String,Integer> map = new HashMap<>();
for (int i = 65; i <= 90; i++) {
      map.put(Character.toString((char) i), 0);
}

answered Feb 25 '14 at 09:39

Samoth

460
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1

ASCII codes (65 and 90) are quite unreadable (magic numbers); better to use char: for(char i = 'A'; i <= 'Z'; ++i) etc – Dmitry Bychenko Feb 25 '14 at 09:41
@DmitryBychenko Can elaborate or give a link to what you mean by magic number in this context? – Subir Kumar Sao Feb 25 '14 at 09:46
@Subir Kumar Sao A "magic number" is a fixed number in the source code, without an explaination why this particular number was used. In this example: What is "65"? Why not "66"? Also see http://en.wikipedia.org/wiki/Magic_number_%28programming%29 – Marco13 Feb 25 '14 at 09:49
@Subir Kumar Sao: When I say that "65" and "90" are "magic numbers" I mean that it's not evident what do they mean (what's "90"?). http://stackoverflow.com/questions/47882/what-is-a-magic-number-and-why-is-it-bad – Dmitry Bychenko Feb 25 '14 at 09:50

jker · Answer 4 · 2018-10-06T11:09:30.623

With io.vavr

public HashMap<String,Integer> alphanumericAlphabet() {
    return CharSeq
            .rangeClosed('0','9')
            .appendAll(CharSeq.rangeClosed('a','z'))
            .appendAll(CharSeq.rangeClosed('A','Z'))
            .map(character ->Tuple.of(
                    character.toString(),
                    Character.getNumericValue(character)
            ))
            .collect(HashMap.collector());
}

score 0 · Answer 5 · edited May 16 '20 at 19:57

0

Use an IntStream to add char's to a map:

IntStream.rangeClosed((int) 'a', (int) 'z').forEach(ch -> map.put((char) ch, 0));

edited May 16 '20 at 19:57

Juan Diego Lozano

989
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18
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answered May 16 '20 at 18:10

Suleman

41
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Fast way to load all alphabetic characters to a hashmap

5 Answers5