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If I have an object implementing the Map interface in Java and I wish to iterate over every pair contained within it, what is the most efficient way of going through the map? If efficiency of looping the keys is a priority for your app, then choose a Map implementation that maintains the keys in your desired order.
Jul 1, 2009 · Also a For-Each loop will throw NullPointerException if you try to iterate over a map that is null, so before iterating you should always check for null references. Method #2: Iterating over keys or values using a For-Each loop. If you need only keys or values from the map, you can iterate over keySet or values instead of entrySet.
Dec 11, 2009 · Maybe you can iterate over the map looking for the keys to remove and storing them in a separate collection. Then remove the collection of keys from the map. Modifying the map while iterating is usually frowned upon. This idea may be suspect if the map is very large.
Feb 25, 2009 · This version works with every Java version that supports generic (i.e. Java 5 and up). Java 10 simplified that by letting variable types be inferred using var: for (var entry : map.entrySet()) { var key = entry.getKey(); var value = entry.getValue(); // do stuff }
May 15, 2012 · I am trying this for some hour but not finding any best approach to achieve iteration of hashmap in reverse order, this is the hashmap I have. Map<Integer, List<String>> map = new
Dec 13, 2014 · The Key of the result map is the key of the input map. The value of the result map ist the Property "name" of My object, ordered by priority. The ordering and extracting the name is not the problem, but I could not put it into the result map. I do it the old Java 7 way, but it would be nice it is possible to use the streaming API.
Oct 27, 2023 · I have a Map() object that I need to iterate, so I can get the day of the week and a selected hour. The code below doesn't work, because Object.keys(newFieldReservationPrice).forEach is trying to loop a Map() object, which seems to make no sense.
Jun 18, 2015 · Iterate over their entries simultaneously. If you just want to iterate over the entries in two maps simultaneously, it's no different than iterating over any other Collection. This question goes into more detail, but a basic solution would look like this:
Apr 9, 2012 · I have a Map which contains a String as it's Key, and a List of Strings as it's Value. I need to iterate over all vlaues contained within each List within the Map. So, first I want to get the Keys, which works: Set<String> keys = theMap.keySet(); This returns me a Set containing all my Keys. Great :)
Create a new map (mapNew). Then iterate over the existing map (mapOld), and add all changed and transformed entries into mapNew. After the iteration is complete, put all values from mapNew to mapOld. This might not be good enough if the amount of data is large though.
