How to sort HashMap by key order?

Question

I would like to have a duplicate copy of an entire hashmap that is sorted by key. The hashmap is of type HashMap. Below is what I did.

SortedSet<String> keys = new TreeSet<String>(unsortedap.keySet());
 for (String key : keys) {
 String value = unsortedMap.get(key);
 // I have noticed that here the key values are in order
 // How do I copy these ordered values to a hashmap?
}

The values seem to be sorted after using TreeSet, however, I am not sure of what to do now. How can I get these values into a new hashmap?

• OldCurmudgeon: new TreeMap(unsortedMap) should work.
• portfoliobuilder: It does not seem to have the new order. After I added the code snippet I printed out the hashmap values and they were the same still. The sortedSet is sorted, but I could not cast that to a Hashmap
• user2336315: @portfoliobuilder An HashMap doesn't retain a "logical" order such as alphabetical for the key. In fact it has no order. You can use TreeMap instead.
• portfoliobuilder: Ok, so this I could use an example of. I have not used a TreeMap before (first time hearing about this)
• OldCurmudgeon: Actually you shoul only specify itz type on creation. From then on use either Map or SortedMap.

Answer 1

The easiest way is just to put the key-value pairs into a TreeMap. Normally this will be ordered by key in default comparator order. If you need custom ordering you can construct the TreeMap with a custom Comparator which implements your preferred ordering.

Instead of your code, just use:

SortedMap<String, String> sortedMap = new TreeMap<>(unsortedMap);

You can be sure a TreeMap will use the same ordering as a TreeSet if only because a TreeSet uses a TreeMap with null values 'under the hood' for its implementation anyway.

• portfoliobuilder: I will accept this answer, and do some research on SortedMaps and TreeMaps. Thanks!