Question

I have a set with multi-dimensional hashmaps, like so:

Set<HashMap<String, HashMap<String, String>>> myHashSet = new HashSet<HashMap<String, HashMap<String, String>>>();

I am having trouble removing a HashMap entry. I know the key for the top level hashmap, but do not know any data in the underlying hashmap. I am trying to remove a hashmap entry in the set in these ways:

I.

Set<HashMap<String, HashMap<String, String>>> myHashSet = new HashSet<HashMap<String, HashMap<String, String>>>();

... Add some hashmaps to the set, then ...

String myKey = "target_key";
setInQuestion.remove(myKey);

II.

Set<HashMap<String, HashMap<String, String>>> myHashSet = new HashSet<HashMap<String, HashMap<String, String>>>();

... Add some hashmaps to the set, then ...

String myKey = "key_one"; //Assume a hashmap has been added with this top level key
HashMap<String, HashMap<String, String>> removeMap = new HashMap<String, HashMap<String, String>>();
HashMap<String, String> dummyMap = new HashMap<String, String>();
removeMap.put(myKey, dummyMap);
setInQuestion.remove(removeMap);

Neither of these methods work. How would I go about removing an entry in the set if I only know the top level hashmap’s key?

Answer 1

Collection.remove() requires object equality. the various jdk Map implementations implement equality to mean all keys/values must match. Since none of the objects you are passing to the remove() call would be “equal” to any of the Maps in the Set, nothing is being removed.

the only way to do what you want is to iterate through the Set yourself to find the matching Map (or, make the Set into a Map keyed on that special key).