How to find the latest date from the given map value in java

learn groovy :

I'm having hash map with below values, in values I've date as string data type. I would like to compare all the dates which is available in map and extract only one key-value which has a very recent date.

I would like to compare with values not keys.

I've included the code below

import java.util.HashMap;
import java.util.Map;

public class Test {

  public static void main(String[] args) {

      Map<String, String> map = new HashMap<>();
      map.put("1", "1999-01-01");
      map.put("2", "2013-10-11");
      map.put("3", "2011-02-20");
      map.put("4", "2014-09-09");

      map.forEach((k, v) -> System.out.println("Key : " + k + " Value : " + v));
    }

}

The expected output for this one is:

Key 4 Value 2014-09-09

WJS :

This should provide the newest (aka largest) date as compared to the others.

      String max = map.values().stream().reduce("0000-00-00",
            (a, b) -> b.compareTo(a) >= 0 ? b
                  : a);

If you also want the key, then do this and return a Map.Entry. Requires Java 9+

         Entry<String, String> ent =
            map.entrySet().stream().reduce(Map.entry("0", "0000-00-00"),
                  (a, b) -> b.getValue().compareTo(a.getValue()) >= 0 ? b
                        : a);

         System.out.println(ent.getKey() + " -> " ent.getValue());

This presumes your map is non-empty. if it is empty, then it returns a null. Works with Java 8+

        Entry<String, String> ent = map.entrySet().stream().reduce(
            (a, b) -> b.getValue().compareTo(a.getValue()) >= 0 ? b
                  : a).orElseGet(() -> null);