Re-arrange HashMap keys in custom pre-defined order

Question

I have an HashMap<String, String> that I need sorted in a specific order. I understand HashMaps, because of how they are constructed, cannot be easily sorted. However, I am looking for the best strategy to re-arrange the keys in my HashMap - for example my current HashMap looks like this:

"folioProperties": {
    "strategy": "Strategy",
    "summary": "Summary",
    "initiative": "Initiative",
    "deliveryMilestone": "Delivery Milestone",
    "onTarget": "On Target",
    "size": "Size",
    "driver": "Driver",
    "issueName": "Issue Name",
    "releaseWindow": "Release Window",
    "type": "Type",
    "targetQuarter": "Target Quarter"
}

I have a table view that shows each of these properties as columns and I need to order the columns/hashmap by Strategy, Initiative, Issue Name, Summary, Delivery Milestone, On Target, Size, Target Quarter, Driver, Type, Release Window .

Any suggestions would be appreciated!

PS Before the HashMap is constructed, the keys are in a List<String> .

Answer 1

It seems that you do not understand the problem that you are attempting to fix. The hashmap is a tool for storing information. It seems likely that you never actually need to sort the hashmap. Instead, it seems likely that you need to display elements in a specific order.

Here are two ways to retrieve the elements from the hashmap in a specific order:

Retrieve the elements in the desired order

blam = map.get("strategy");
... do something with blam.

blam = map.get("Initiative");
... do something with blam.

... repeat for all elements.

Sort the keys then retrieve them in order

keyList.addAll(map.keySet());
Collections.sort(keyList, yourComparator);
for (final String current : keyList)
{
    blam = map.get(current);
    ... do something with blam.
}

Stop representing an object as a Map

Build a class, perhaps named FolioProperties, that represents the properties of the Folio.

public class FolioPropertiesFND
{
    private String initiative;
    private String strategy;
    ... one field per property.

    public String getInitiative()
    {
        return initiative;
    }

    public void setInitiative(final String newValue)
    {
        initiative = newValue;
    }
}

Answer 2

If your data is in an ordered list prior to the map construction, then what you need is a java.util.LinkedHashMap

from the javadoc:

Hash table and linked list implementation of the Map interface, with predictable iteration order. This implementation differs from HashMap in that it maintains a doubly-linked list running through all of its entries. This linked list defines the iteration ordering, which is normally the order in which keys were inserted into the map (insertion-order).

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

If you use a LinkedHashMap, then all you have to do is to put the key/value pairs in the correct order and the map will ensure the same iteration order for you.