How sort an ArrayList of HashMaps holding several key-value pairs each?

Question

I need to call an external API with an ArrayList of HashMaps holding several predefined key-value pairs each. An example:

ArrayList

        

Answer 1

You need to implement a Comparator> or more generally Comparator> which just extracts the value assocated with the value key, then use Collections.sort. Sample code (with generalization for whatever key you want to sort on):

class MapComparator implements Comparator>
{
    private final String key;

    public MapComparator(String key)
    {
        this.key = key;
    }

    public int compare(Map first,
                       Map second)
    {
        // TODO: Null checking, both for maps and values
        String firstValue = first.get(key);
        String secondValue = second.get(key);
        return firstValue.compareTo(secondValue);
    }
}

...
Collections.sort(arrayListHashMap, new MapComparator("value"));