retainAll for Map<String, String>

[Paolo Pinkel]

I have some TreeMaps and I need to do a retainAll. In the end, I want a TreeMap made out of the key-value-pairs that were the same for every TreeMap.

Any idea? It's not just that the keys need to be equal... it needs to be the key and the value. That's why I don't know how to handle the .keySet and .values.

Thanks!

[Wouter Oet]

Didn't test it out but: do a retainAll on the keys then a retainAll on the values and check whether the size of the set has changed.
Flaw in my logic.

[Wouter Oet]

Get the entry sets and do a retailAll on those.

[Paolo Pinkel]

This will not check if keys andvalues are the same. Only the keys.

[Rob Spoor]

The entry set will definitely check for both. It will use Map.Entry equality which says that two entries are equal only if both the keys and values are equal. So if a key has one value in the first map and a different value in the second map, their entries for that key will be different and retainAll will not retain that entry.

[Paolo Pinkel]

This is how I try it:

Map<String, String> finalMap = new TreeMap<String, String>();
		if(!tempMaps.isEmpty()) {
			finalMap = tempMap.get(0);			
			for(Map<String, String> someMap : tempMaps) {
				 finalMap.keySet().retainAll(someMap.keySet());
			}
		}

tempMaps is a list of Map<String, String>. In the end, I want to have a map with the retainAll values of every Map.

Can you see why it won't work?

Your help is much appreciated!

[Paolo Pinkel]

Argh! I confused keySet and entrySet. Now it works. Thanks everyone!