Java 8 Map of Collections remove element for collection and remove entry if empty

  • A+
Category:Languages

I have a map for which the values are a collection. Given a key, I want to remove an element of the collection and return it, but I also want to remove the entry if the collection is empty. Is there a way to do this in a short way using one of the numerous new Map methods of Java 8?

One easy example (I use a Stack but it could be a List, a Set, etc.). For the sake of the example, let's say that it is already checked that the map contains the key.

public static String removeOne(Map<Integer, Stack<String>> map, int key) {     Stack<String> stack = map.get(key);     String result = stack.pop();     if(stack.isEmpty()){         map.remove(key);     }     return result; } 

I tried doing something like

map.compute(1, (k, v) -> {v.pop(); return v.size() == 0 ? null : v;}); 

But even though it does indeed remove the entry if empty, I don't know how to get the value returned by pop().

 


Well, it's even uglier than what you have already in place, but there is a way, I guess:

public static String removeOne(Map<Integer, Stack<String>> map, int key) {     String[] removed = new String[1];     map.compute(key, (k, v) -> {         removed[0] = v.pop();         return v.size() == 0 ? null : v;     });     return removed[0]; } 

Problem is that merge/compute and the like return the value, and in your case that is a Stack/Set/List, not and individual element from that collection.

Comment

:?: :razz: :sad: :evil: :!: :smile: :oops: :grin: :eek: :shock: :???: :cool: :lol: :mad: :twisted: :roll: :wink: :idea: :arrow: :neutral: :cry: :mrgreen: