Does a TreeMap's entrySet() return a TreeSet

java collections treemap
Emil picture Emil · Aug 26, 2010 · Viewed 7.8k times · Source

Does the entrySet() function that is called from a treemap instance return a TreeSet of entry's or simply a set of entry's.Is the order ensured?

Instead of getting it as a set of entry's how can a get a list of entry's in order?

Answer

Sean Patrick Floyd picture Sean Patrick Floyd · Aug 26, 2010

It's the other way around: a TreeSet uses a TreeMap internally. (See first sentence of the TreeSet docs)

There's not much Sun java source code I can find on the web to link to, but here are some oldish versions:

As you can see, TreeMap defines an inner class called TreeMap.EntrySet which just extends AbstractSet. And no, it does not implement SortedSet (which would otherwise probably be specified by the SortedMap.entrySet() contract).

But to answer the actual question: yes, the order is ensured as specified in the SortedMap.entrySet() contract.

Update: JavaDoc links updated for Java 8, sources are still Java 6

Related questions

How to iterate over a TreeMap?

Possible Duplicate: How do I iterate over each Entry in a Map? I want to iterate over a TreeMap, and for all keys which have a particular value, I want them to be added to a new TreeMap. How can …

Read More
Java List Sorting: Is there a way to keep a list permantly sorted automatically like TreeMap?

In Java you can build up an ArrayList with items and then call: Collections.sort(list, comparator); Is there anyway to pass in the Comparator at the time of list, creation like you can do with TreeMap? The goal is …

Read More
Why and when to use TreeMap

Could someone tell me when and why to use TREEMAP.I went through This link but didn't find my answer. As Per my thinking we use treemap to get the data sort according to your key and the same we …

Read More