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

Question

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

Answer 1

Use Collections.max with entrySet

Entry<String, String> max = Collections.max(map.entrySet(), Map.Entry.comparingByValue());

or

Entry<String, String> max = Collections.max(map.entrySet(),
    new Comparator<Entry<String, String>>() {
        @Override
        public int compare(Entry<String, String> e1, Entry<String, String> e2) {
            return LocalDate.parse(e1.getValue()).compareTo(LocalDate.parse(e2.getValue()));
        }
});

Answer 2

This should work

    Optional<Map.Entry<String, String>> result = map.entrySet().stream().max(Comparator.comparing(Map.Entry::getValue));
    System.out.println(result);

output is Optional[4=2014-09-09]