Can we add element in HashMap while iterating?
Is there any way out if we need to change or add a new element into it while iterating or can we get a listiterator on a HashMap. No, you can’t; if you try this, you will get a ConcurrentModificationException when you use the iterator after modifying the map.
Can we update HashMap 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 …
What happens if we add an entry into a HashMap having a key that already exists?
What happens if we put a key object in a HashMap which exists? Explanation: HashMap always contains unique keys. If same key is inserted again, the new object replaces the previous object.
Can we remove element from HashMap while iterating?
You cannot remove an entry while looping over Map but you can remove a key or value while iterating over it. Since Iterator of HashMap is fail-fast it will throw ConcurrentModificationException if you try to remove entry using Map.
How do you remove while iterating?
The right way to remove objects from ArrayList while iterating over it is by using the Iterator’s remove() method. When you use iterator’s remove() method, ConcurrentModfiicationException is not thrown.
Can I remove key from HashMap while iterating?
While iterating, check for the key at that iteration to be equal to the key specified. The entry key of the Map can be obtained with the help of entry. getKey() method. If the key matches, remove the entry of that iteration from the HashMap using remove() method.
What is HashMap What will happen if I insert duplicate in the HashMap which will be overridden key or value?
If you try to insert the duplicate key, it will replace the element of the corresponding key. HashMap is similar to HashTable, but it is unsynchronized. It allows to store the null keys as well, but there should be only one null key object and there can be any number of null values.
What will happen if we add duplicate in Set?
If we insert duplicate values to the Set, we don’t get any compile time or run time errors. It doesn’t add duplicate values in the set. Below is the add() method of the set interface in java collection that returns Boolean value either TRUE or FALSE when the object is already present in the set.
How do you remove a mapping while iterating over HashMap in Java?
How to delete an entry from a HashMap during Iteration
- Get a Set of keys or Set of entries by calling keySet() or entrySet() method of java.util.Map.
- Get the Iterator from the key set or entry set.
- Iterate over key set or entry set.
- Check each value, if it satisfies criterion call iterator.remove() method.
How do you avoid concurrent modification exception?
How to avoid ConcurrentModificationException in a multi-threaded environment?
- We can iterate over the array instead of iterating over the collection class.
- Locking the list by putting it in the synchronized block is another way to avoid the concurrent modification exception.
What are the advantages of using a Java HashMap?
Advantages of HashMap When you add items to a HashMap, you are not guaranteed to retrieve the items in the same order you put them in. The purpose of a map is to store items based on a key that can be used to retrieve the item at a later point. Collection functionality some great utility functions are available for lists via the Collections class.
How to iterate in a hashtable?
Using Enumeration Interface
How does HashMap differ from hashtable in Java?
HashMap is non synchronized. It is not-thread safe and can’t be shared between many threads without proper synchronization code.
Is it possible to return a hashmap object in Java?
Is it possible to return a HashMap object in Java?, Yes. It is easily possible, just like returning any other object: public Map mapTheThings (String keyWord, String certainValue) { Map