The order of elements in the HashMap Java

Question

HashMap<Integer, String> map = new HashMap<Integer, String>();
map.put(5,a);
map.put(4,b);
map.put(3,c);
map.put(2,d);
map.put(1,e);
System.out.println(map);

Why the result is equal {1=e, 2=d, 3=c, 4=b, 5=a}?

if you need a stort order in your map, you need a [SortMap](http://docs.oracle.com/javase/6/docs/api/java/util/SortedMap.html) — Jens, May 23 '14 at 11:48

score 3 · Answer 1 · answered May 23 '14 at 11:45

3

Java HashMap doesn't keep any order. API says

This class makes no guarantees as to the order of the map; in particular, it does not guarantee that the order will remain constant over time.

answered May 23 '14 at 11:45

Abimaran Kugathasan

31,165
11
75
105

"So, try some times, you will get different order of printing the content." It's also not guaranteed that it will be different. Are you sure that bogus orderings aren't returned deterministically? – nanofarad May 23 '14 at 11:48
@hexafraction : Not sure, I guess it, removed those lines – Abimaran Kugathasan May 23 '14 at 11:49

score 0 · Answer 2 · answered May 23 '14 at 11:47

From HashMap's javadoc:

This class makes no guarantees as to the order of the map; in particular, it does not guarantee that the order will remain constant over time.

A LinkedHashMap would suffice for ordering by insertion order, and a TreeMap may be used when order through a key's comparator is needed.

The order of elements in the HashMap Java

2 Answers2