Java 8 HashMap KeySet() output different from Java 7

Question

I upgraded from Java 7 to Java 8 and noticed Junit failures in places where the keySet() of HashMap was used.

Map<String, String> map = new HashMap<String, String>();
map.put("var1".toUpperCase(), "var");
map.put("var".toUpperCase(), "var1");
Set<String> varKeys = replacementMap.keySet();

In Java 7:

varKeys=[VAR,VAR1]

In Java 8:

varKeys=[VAR1,VAR]

Any help on this?

`Set` and `Map` are unorderer collections by definition. The output is correct in both cases. — Crozin, Aug 01 '16 at 09:14
What is the JUNIT test case you have written ? The order is not guaranteed in a HashMap/Set , You can try a TreeSet if order needs to be guaranteed. — Ramachandran.A.G, Aug 01 '16 at 09:15

score 15 · Answer 1 · edited Aug 01 '16 at 09:38

15

HashMap does not guarentee order of keys. If your Junit test relied on the order of keys, then it is designed incorrectly.

edited Aug 01 '16 at 09:38

Manu

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answered Aug 01 '16 at 09:15

Sharon Ben Asher

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score 6 · Answer 2 · answered Aug 01 '16 at 09:14

I suggest using LinkedHashMap instead if you want to preserve insertion order.

The order of HashMap isn't defined and isn't consistent. i.e. the same keys can appear in different orders. The implementation of HashMap changed between Java 7 and Java 8 significantly so you should expect the order to be different in some cases.

score 3 · Answer 3 · answered Aug 01 '16 at 09:14

3

Set doesn't guarantee order of elements. If you need ordered hashmap, you can use LinkedHashMap

answered Aug 01 '16 at 09:14

TheKojuEffect

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agilob · Answer 4 · 2018-02-05T18:09:43.817

3

That's a HashSet/HashMap, where order is never guaranteed and can change at any time. What you want is TreeSet or LinkedHashSet, learn here about differences.

edited Feb 05 '18 at 18:09

answered Aug 01 '16 at 09:15

agilob

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Java 8 HashMap KeySet() output different from Java 7

4 Answers4