How do I find the most recent joda DateTime in map?

EiteWald :

I have a map that is updated from Firebase Realtime Database, so I don't know the map size in advance.

In the map I have a String as key, and a Joda DateTime as value.

I don't know how to iterate through the map to return the most recent Datetime.

I'll try to explain better:

//on returning results from Realtime Database
  Map<String, DateTime> myMap = new HashMap<>();

    if(dataSnapshot.exists){

       for(DataSnapshot data:dataSnapshot.getChildren()){

           String key = data.getKey();
           DateTime dateTime = // I get the data and convert it to Datetime; no problem here; I can do it.

           myMap.put(key, dateTime);

       }

   //outside the Loop
   //HERE IS WHAT I NEED HELP WITH

      for(DateTime date:myMap.values()){

         // 1 - check if date is after the next date in map
         // 2 - if it is, then keep it
         // 3 - if it is not, then remove
         // 4 - in the end, only one pair of key/value with the most recent date is left

      }

    }

Can you guys please, help me? Thank you so much

EDIT: Sorry, one more thing. I'm using a minimum sdk in Android that doesn't ler me use Java 8. I have to use Java 7 features.

Andreas :

how to iterate through the map to return the most recent Datetime

Java 8+ using Streams:

// To get latest key (or entry)
String latestKey = myMap.entrySet().stream()
        .max(Entry::comparingByValue)
        .map(Entry::getKey) // skip this to get latest entry
        .orElse(null);

// To get latest value
DateTime latestValue = myMap.values().stream()
        .max(Comparator.naturalOrder())
        .orElse(null);

Any Java version using for loop:

Entry<String, DateTime> latestEntry = null;
for (Entry<String, DateTime> entry : myMap.entrySet()) {
    if (latestEntry == null || entry.getValue().isAfter(latestEntry.getValue()))
        latestEntry = entry;
}
String latestKey = (latestEntry != null ? latestEntry.getKey() : null);

In the above, adjust as needed depending on whether you need latest key, value, or entry (key+value).

---

in the end, only one pair of key/value with the most recent date is left

Best way is to replace the map, or at least replace the content, after finding the latest entry.

Java 8+ using Streams (replacing map):

myMap = myMap.entrySet().stream()
        .max(Comparator.comparing(Entry::getValue))
        .stream().collect(Collectors.toMap(Entry::getKey, Entry::getValue));

Any Java version using for loop (replacing content):

Entry<String, DateTime> latestEntry = null;
for (Entry<String, DateTime> entry : myMap.entrySet()) {
    if (latestEntry == null || entry.getValue().isAfter(latestEntry.getValue()))
        latestEntry = entry;
}
myMap.clear();
if (latestEntry != null)
    myMap.put(latestEntry.getKey(), latestEntry.getValue());