Compare two HashMap in Java

Question

How to fetch the HashMap based on Max-key field

Eaxmple:-

        List<Map<String, Integer>> data = new ArrayList<Map<String, Integer>>();
        Map<String, Integer> map1 = new HashMap<>();
        map1.put("A", 10);
        map1.put("B", 15);
        map1.put("C", 20);

        Map<String, Integer> map2 = new HashMap<>();
        map2.put("A", 20);
        map2.put("B", 30);
        map2.put("C", 50);

        Map<String, Integer> map3 = new HashMap<>();
        map3.put("A", 50);
        map3.put("B", 60);
        map3.put("C", 70);

        data.add(map1);
        data.add(map2);
        data.add(map3);

Here I have 3 maps that I'm storing in the List.

Now I want to filter a map based on max A key value.

In the above map3 A value has the max integer value.

Expected out is:-

In the last only the map3 should present inside the List.

Is it possible to filter using java8?

Any suggestions would be helpful

Answer 1

I finally able to do this with help of comparator

Here is the code that will filter based filtering based on max date:-

Result is stored in the firstMap variable...

import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.ArrayList;
import java.util.Date;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

public class Main {

    public static void main(String args[]) throws ParseException {
        Map<String, String> s = test();
        System.err.println(s.toString());

    }

    public static Map<String, String> test() throws ParseException {
        List<Map<String, String>> data = new ArrayList<Map<String, String>>();
        Map<String, String> map1 = new HashMap<>();
        map1.put("A", "2021-03-08");

        Map<String, String> map2 = new HashMap<>();
        map2.put("A", "2021-03-23");

        Map<String, String> map3 = new HashMap<>();
        map3.put("A", "2021-03-21");

        data.add(map1);
        data.add(map2);
        data.add(map3);

        SimpleDateFormat si = new SimpleDateFormat("yyyy-MM-dd");
        Date firstMax = si.parse(data.get(0).get("A"));

        Map<String, String> firstMap = data.get(0);

        for (Map<String, String> map : data) {

            Date loopMax = si.parse(map.get("A"));
            if (firstMax.compareTo(loopMax) < 0) {
                firstMax = loopMax;
                firstMap = map;
            }
        }
        return firstMap;

    }
}

Output:-

{A=2021-03-23}