HashMap borks my values

Question

HashMap<String, int[]> H = new HashMap<String, int[]>(); 
H.put("drdetroit", new int[]{1,2});
H.put("drdetroit", new int[]{1,3}); 
System.out.println(H.get("drdetroit").toString());

It prints out

[I@c3c749

I assume this is the hashed value(is it?). How can I make it print my actual values?

If you want to print the values of an array using `toString()` on that array, you will get something completely different from the values, it does not matter if it is in a HashMap or not. Use `Arrays.toString(array)` instead — andreih, Dec 05 '12 at 10:06
Also your hashmap will only print the first value so don't get confused. :) — Henrik Andersson, Dec 05 '12 at 10:08
You have to change the second key to something unique since HashMaps stores only unique keys. So `H.put('drdetroit', value);` and `H.put('drchicago', value);` will work for you — Henrik Andersson, Dec 05 '12 at 10:10
@limelights: Is there an object that I can use that allows multiple values per key? — Wuschelbeutel Kartoffelhuhn, Dec 05 '12 at 10:11
Nah, but you can do a map with a list. So `HashMap> H = new HashMap>();` and then add the values to the list. I'll post an answer for you to see. — Henrik Andersson, Dec 05 '12 at 10:12
@limelights If he stores an array of `int`, wouldn't he need a `List` instead of a `List` of arrays of `int` ? — andreih, Dec 05 '12 at 10:16
I'm guessing he needs the arrays for something so the List can store the int array just fine. There are perhaps better ways of doing it but I'm working off his example now. :) — Henrik Andersson, Dec 05 '12 at 10:18
Possible duplicate of [How do I print my Java object without getting "SomeType@2f92e0f4"?](http://stackoverflow.com/questions/29140402/how-do-i-print-my-java-object-without-getting-sometype2f92e0f4) — Kevin Panko, Dec 16 '15 at 22:06

score 2 · Answer 1 · edited Dec 16 '15 at 22:04

2

You use Arrays.toString(H.get("drdetroit"));

edited Dec 16 '15 at 22:04

Kevin Panko

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answered Dec 05 '12 at 10:05

Shark

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this prints only the first value not the second one – Wuschelbeutel Kartoffelhuhn Dec 05 '12 at 10:08
That is because a Map can only have 1 value per key, you override the first with the second – Aviram Segal Dec 05 '12 at 10:09
@Aviram Segal: Is there an object that I can use that allows multiple values per key? – Wuschelbeutel Kartoffelhuhn Dec 05 '12 at 10:10
Apache commons collections got a MultiValueMap http://commons.apache.org/collections/apidocs/org/apache/commons/collections/map/MultiValueMap.html – Aviram Segal Dec 05 '12 at 10:11
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`HashMap>` ? you could maybe try this one. – andreih Dec 05 '12 at 10:12
Guava's [`ListMultimap`](https://code.google.com/p/guava-libraries/wiki/NewCollectionTypesExplained#Multimap) is one generics-enabled solution. – Louis Wasserman Dec 05 '12 at 17:49

score 2 · Accepted Answer · answered Dec 05 '12 at 10:17

This is what you're after I believe. Since a HashMap can only store unique keys you're forced to go with a list if you want multiple values for one (1) key.

There are perhaps better ways of achieving this but it's working and is pretty expressive in itself and pretty clear what it does and how.

The HashMap now accepts the List interface and can thusly accept any list-type that implements it. Which is pretty neat! :)

ArrayList<int[]> values = new ArrayList<int[]>();

values.add(new int[]{1,2});
values.add(new int[]{1,3});

HashMap<String, List<int[]>> H = new HashMap<String, List<int[]>>(); 

H.put("drdetroit", values);

for(String key : H.keySet()) {
    for(int[] array : H.get(key)){
        System.out.println(Arrays.toString(array));
    }
}

score 1 · Answer 3 · answered Dec 05 '12 at 10:06

1

System.out.println(Arrays.toString(H.get("drdetroit")));

I - stands for int array and c3c749 is hashcode

answered Dec 05 '12 at 10:06

Narendra Pathai

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c3c749 is not hashCode, it is memory address. I@c3c749 is read as Integer at c3c749. – Damian Leszczyński - Vash Dec 05 '12 at 10:27
@Vash look at Quoi's answer – Narendra Pathai Dec 05 '12 at 10:41
@NarendraPathai, My mistake. That is hex of hash. – Damian Leszczyński - Vash Dec 05 '12 at 10:53

score 0 · Answer 4 · answered Dec 05 '12 at 10:05

0

Because you try to make a String out of an array!

You could do for example:

String myArray = H.get("drdetroit");
System.out.println(myArray[0]);

answered Dec 05 '12 at 10:05

cruxi

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Mm, no, he just prints it's object value. – Shark Dec 05 '12 at 10:06

score 0 · Answer 5 · answered Dec 05 '12 at 10:08

Try this to print array values -

System.out.println(Arrays.toString(H.get("drdetroit")));

H.get("drdetroit").toString() returns array class name and @ and hashcode in hexString.

public String toString() {
    return getClass().getName() + "@" + Integer.toHexString(hashCode());
}

HashMap borks my values

5 Answers5