How to iterate a HashMap using the natural entrySet() order?

Question

My Map contains keys sorted in alphabetical order. When I display it, I'm using entrySet().iterator(), but my results are not in the alphabetical order. How can I get my results in order?

Answer 1

No, your map does not hold elements in alphabetical order. You may have .put(..) then in that order, but the map does not have a defined iteration order.

Others suggest using SortedSet, but you can also use LinkedHashMap. It guarantees iteration order:

This implementation (LinkedHashMap) spares its clients from the unspecified, generally chaotic ordering provided by HashMap (and Hashtable), without incurring the increased cost associated with TreeMap

Answer 2

Use TreeMap:

A Red-Black tree based NavigableMap implementation. The map is sorted according to the natural ordering of its keys, or by a Comparator provided at map creation time, depending on which constructor is used...

Answer 3

For anyone finding this question in 2020 and beyond...
Now that we have streams, you can do something like this:

map.entrySet()
  .stream()
  .sorted(Map.Entry.comparingByKey())
  .forEach(System.out::println);

Answer 4

My Map contains keys sorted in alphabetical order

This is not true.

Use http://download.oracle.com/javase/6/docs/api/java/util/SortedMap.html or sort your keys before iterate