Can we iterate HashMap?

There is a numerous number of ways to iterate over HashMap of which 5 are listed as below: Iterate through a HashMap EntrySet using Iterators. Iterate through HashMap KeySet using Iterator. Iterate HashMap using for-each loop.

Is it possible to iterate through a HashMap?

In Java HashMap, we can iterate through its keys, values, and key/value mappings.

How many ways we can iterate HashMap in Java?

There are generally five ways of iterating over a Map in Java.

How does HashMap iteration work?

The entrySet() method is used to get a Set view of the mappings contained in this map. So, this will return you the set representation of values stored in the Map but this is linked with Map so during iteration of Map if you change anything it will be reflected in Set.

Can you iterate through a HashTable in Java?

There are various ways by which we can iterate through the HashTable which are as follows: Using Enumeration Interface. Using keySet() method of Map and Enhance for loop. Using keySet() method of Map and Iterator Interface.

5 Best Ways to Iterate Over HashMap in Java

What is the difference between HashMap and Hashtable?

Hashmap vs Hashtable

It is thread-safe and can be shared with many threads. HashMap allows one null key and multiple null values whereas Hashtable doesn't allow any null key or value. HashMap is generally preferred over HashTable if thread synchronization is not needed.

How a hash table can change the iterator?

Hashtable will change the iterator by using Enumerator interface.

How do you make a HashMap iterator?

Can we add a new entry to HashMap while iterating?

You need to use ConcurrentHashMap to add elements while iterating the collection. HashMap uses fail-fast iterator, which throws ConcurrentModificationException when the collection is updated while iterating.

Can HashMap have duplicate keys?

HashMap stores key, value pairs and it does not allow duplicate keys. If the key is duplicate then the old key is replaced with the new value.

What is the best way to iterate over a HashMap?

What is difference between Iterator and ListIterator?

An Iterator is an interface in Java and we can traverse the elements of a list in a forward direction whereas a ListIterator is an interface that extends the Iterator interface and we can traverse the elements in both forward and backward directions.

Can we use comparator with HashMap in Java?

Sort HashMap by Values using Comparator Interface

To sort the HashMap by values, we need to create a Comparator. It compares two elements based on the values. After that get the Set of elements from the Map and convert Set into the List. Use the Collections.

What is keySet in HashMap?

HashMap keySet() Method in Java

HashMap. keySet() method in Java is used to create a set out of the key elements contained in the hash map. It basically returns a set view of the keys or we can create a new set and store the key elements in them. Syntax: hash_map.keySet()

What is entrySet in map in Java?

entrySet() method in Java is used to create a set out of the same elements contained in the hash map. It basically returns a set view of the hash map or we can create a new set and store the map elements into them. Syntax: hash_map.entrySet()

What is LinkedHashMap in Java?

The LinkedHashMap class of the Java collections framework provides the hash table and linked list implementation of the Map interface. The LinkedHashMap interface extends the HashMap class to store its entries in a hash table. It internally maintains a doubly-linked list among all of its entries to order its entries.

Can we remove from HashMap while iterating?

You should always use Iterator's remove() method to remove any mapping from the map while iterating over it to avoid any error.

What is difference between ConcurrentHashMap and HashMap?

HashMap is non-Synchronized in nature i.e. HashMap is not Thread-safe whereas ConcurrentHashMap is Thread-safe in nature. HashMap performance is relatively high because it is non-synchronized in nature and any number of threads can perform simultaneously.

Can we remove element from HashMap while iterating?

Remove elements from HashMap while Iterating using KeySet

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.

What is difference between HashMap and TreeMap?

HashMap allows a single null key and multiple null values. TreeMap does not allow null keys but can have multiple null values. HashMap allows heterogeneous elements because it does not perform sorting on keys. TreeMap allows homogeneous values as a key because of sorting.

What is the difference between HashMap and HashSet?

HashMap Stores elements in form of key-value pair i.e each element has its corresponding key which is required for its retrieval during iteration. HashSet stores only objects no such key value pairs maintained. Put method of hash map is used to add element in hashmap.

Are Hashmaps ordered?

HashMap is implemented as a hash table, and there is no ordering on keys or values. TreeMap is implemented based on red-black tree structure, and it is ordered by the key.

What is the advantage of hash table over array?

Searching over a data structure such as an array presents a linear time complexity of O(n). In other words, as the data structure increases in size, the search time increases in a linear fashion. Simply put, using a hash table is faster than searching through an array.

What is difference between Hashtable and ConcurrentHashMap in Java?

Hashtable is belongs to the Collection framework; ConcurrentHashMap belongs to the Executor framework. Hashtable uses single lock for whole data. ConcurrentHashMap uses multiple locks on segment level (16 by default) instead of object level i.e. whole Map . ConcurrentHashMap locking is applied only for updates.

What is load factor in HashMap?

The load factor is the measure that decides when to increase the capacity of the Map. The default load factor is 75% of the capacity. The threshold of a HashMap is approximately the product of current capacity and load factor. Rehashing is the process of re-calculating the hash code of already stored entries.