Convert HashMap to ArrayList with identical sort

Question

I have the following problem: I have a HashMap

HashMap <String, BeanRelEstatisticaMateriaPrima> dataBeanList = new HashMap ();

And I am generating an iReport report, but to send the data to the report, I do a HashMap conversion to an ArrayList:

List <BeanRelEstatisticaMateriaPrima> test = new ArrayList <BeanRelEstatisticaMateriaPrima> (dataBeanList.values ());

JRBeanCollectionDataSource beanColDataSource = new JRBeanCollectionDataSource (test);

But in doing this conversion, ordination is being lost. In the hashmap I have in alphabetical order, eg: (A, B, C, D, E) but in the ArrayList it gets (D, A, E, C, B)

Is there a way to transform to ArrayList by keeping the sort order exactly the same as HashMap?

"In the hashmap I have in alphabetical order" I'm not convinced you do. Hashmaps have no ordering guarantee. Perhaps you insert them in that order; however, they will be inserted into the list in the iteration order. — Andy Turner, Sep 26 '18 at 20:26
@gawi no, it doesn't. It orders according to either natural order, or a provided comparator. — Andy Turner, Sep 26 '18 at 20:37
you might be right, I'm using it to have deterministic order, but never paid attention if it's insertion order, thx for pointing it out — gawi, Sep 26 '18 at 20:39
Thanks to all for your help. I used LinkedHashMap and it was correct. Thank you. — Geizon T., Sep 26 '18 at 21:02

score 2 · Accepted Answer · answered Sep 26 '18 at 20:26

2

HashMaps do not guarantee order. Use a LinkedHashMap if you want to preserve order of insertion.

answered Sep 26 '18 at 20:26

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Thanks to all for your help. I used LinkedHashMap and it was correct. Thank you. – Geizon T. Sep 26 '18 at 21:02

Convert HashMap to ArrayList with identical sort

1 Answers1