Can we add elements while iterating?

Can we add elements while iterating?

3 Answers. You can’t modify a Collection while iterating over it using an Iterator , except for Iterator. remove() . This will work except when the list starts iteration empty, in which case there will be no previous element.

Can we modify Map while iterating?

Well, you can’t do it by iterating over the set of values in the Map (as you are doing now), because if you do that then you have no reference to the keys, and if you have no reference to the keys, then you can’t update the entries in the map, because you have no way of finding out which key was associated with the …

Can we add a new entry to HashMap while iterating?

You need to consider what it means to put a value to a Map whilst iterating. HashMap defines no order over which its entries will be iterated over. So when you put a new entry, should the entry be returned by the iterator later or not. Consistency of behaviour is important.

Can you add to an ArrayList while iterating?

3. ArrayList listIterator() – Add/Remove. ListIterator supports to add and remove elements in the list while we are iterating over it.

Which is the correct way to delete a key from a Map?

How to delete an entry from a HashMap during Iteration

1. Get a Set of keys or Set of entries by calling keySet() or entrySet() method of java.util.Map.
2. Get the Iterator from the key set or entry set.
3. Iterate over key set or entry set.
4. Check each value, if it satisfies criterion call iterator.remove() method.

How do you prevent ConcurrentModificationException on a Map?

use ConcurrentHashMap. keep on using simple HashMap, but build a new map on each modification and switch maps behind the scenes (synchronizing the switch operation or using AtomicReference)

In what order are HashMap mappings stored?

In which order mappings are stored in HashMap? (answer) Random order because HashMap doesn’t provide any ordering guarantee for keys, values, or entries. When you iterate over a HashMap, you may get a different order every time you iterate over it.

Can you remove elements from a list while iterating?

In addition to my previous answer here, the documentation says that you should not remove elements of a current collection: To remove elements while iterating a list, create a new list, then copy the elements you wish to keep.

How to iterate over and remove from a map in Java?

ConcurrentMap running = create and populate map Set > set = running.entrySet (); for (Entry entry : set) { if (entry.getKey ()>600000) { set.remove (entry.getKey ()); } } Maybe you can iterate over the map looking for the keys to remove and storing them in a separate collection.

How to remove elements from HashMap while iterating?

Let’s create a HashMap of String as Key and Integer as value and add some elements into it i.e. keyset () method of HashMap returns a set of keys in the HashMap and its backed by HashMap i.e. any items removed from the Key Set will be removed from HashMap too.

Is it good idea to add / remove items from a map?

Size before the loop shows 20, each Opportunity is still available in the Opp loop variable for the entire iteration of the loop after being removed from the Map, size after the loop shows 10. Is it a good idea to add/remove items from a Map as we iterate over it?