How to sort map inside of List in java

Question

 List<Map<String,String>> consolidErr = new LinkedList<Map<String,String>>();

 Map m1= new HashMap<String,String>();
 m1.put("id","1");
 m1.put("value","value1");

 Map m2= new HashMap<String,String>();
 m2.put("id","2");
 m2.put("value","value2");

 Map m3= new HashMap<String,String>();
 m3.put("id","3");
 m3.put("value","value3");

add all m1,m3 and m2 in list

then sort maps based on ids in map now i want maps in list as m1,m2 and m3.

Now I want to sort based on the ids in the map, I did that using iteration of list and keep first id of map as checker and compare with next it works if there any other better way than that using built-in methods.?Please give your ideas.am using bubble sort for this now.

@RohitJain thanks for reply but based on which object of map it will be sorted id or value of map.? — Jericho
– Jericho, Commented Feb 11, 2013 at 4:50

Steve B. · Accepted Answer · 2013-02-11 04:53:28Z

4

The simplest way to do this in java (or at least, with the least mess) is to use a custom comparator.

The idea is that if you have objects with a natural sort (anything that extends Comparable) you can just ask for the sorting , e.g.

Collections.sort(List<Integer> ..

otherwise you can just pass in a Comparator that describes how you want objects compared, with any custom logic you want, e.g. (roughly - this is off the top of my head and doesn't have error checking, but should be enough to give you the idea) -

List<Map<String,String>> consolidErr = ...
enter code here
Collections.sort(consolidErr, new Comparator<Map<String,String>>(){
     public int compare(Map<String,String> a, Map<String,String> b){ 
        return a.get("id").compareTo(b.get("id"));}
    })

answered Feb 11, 2013 at 4:53

Steve B.

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sparker · Accepted Answer · 2017-11-22 14:25:40Z

1

In Java 8, we can sort the list of maps in a single line.

list.sort(Comparator.comparing((Map<String,String> mp) -> mp.get("Id")));

answered Nov 22, 2017 at 14:25

sparker

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Olimpiu POP · Accepted Answer · 2013-02-11 12:53:12Z

0

I would use instead the PriorityQueue

as a wrapper for your list. By providing the Comparator to the constructor when creating it, would assure you that your list will remain sorted after each insertion of a new element to the list.

answered Feb 11, 2013 at 12:53

Olimpiu POP

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