#Hashmap java code

However, The Enumeration returned by Hashtable doesn’t have this behaviour. Thus, in the face of concurrent modification, the iterator fails fast and cleanly, rather than risking undesirable behaviour. It throws ConcurrentModificationException if any thread other than the iterator’s remove() method tries to modify the map structurally.

Iterator in HashMap is a fail-fast iterator.

HashMap is traversed by Iterator while Hashtable can be traversed by both Iterator and the legacy Enumeration.

HashMap allows one null key and multiple null values whereas Hashtable doesn’t allow null values.

Because of synchronization and thread safety, Hashtable is much slower than HashMap if used in single threaded environment.

On the other hand, Hashtable is thread safe, and therefore can be shared between multiple threads. The primary difference between HashMap and Hashtable is that HashMap is not thread-safe, and therefore cannot be shared between multiple threads without external synchronization.

#Hashmap java code

The key is then hashed, and the resulting hash code is used as the index at which the value is stored within the table.

To store an element in a Hashtable or HashMap, you need to specify a key object and its associated value. On the other hand, Hashtable inherits the Dictionary class and also implements the Map interface.Īs both Hashtable and HashMap implements Map, they are similar as both stores key-value pairs where the keys are unique and stored as hash values. HashMap extends the AbstractMap class and implements the Map interface. A Map stores key-value pairs where duplicate keys are not allowed. HashMap and Hashtableīoth HashMap and HashTable implements the Map interface, a sub interface of the Collection interface. In this post, I’ll take up two other implementations that although appears identical, but are inherently different. I have written a post on ArrayList vs LinkedList that explains the nuances of them. Some groups of implementations are similar in the operations they perform, and it is common for novice programmers to use them interchangeably.ĪrrayList and LinkedList are two such implementations that are often confused and incorrectly applied in applications. In the following example, we want to insert three (Key, Value) pair in the HashMap.The Java collection framework provides several collection implementations to store and operate on objects. The default size of HashMap is 16 (0 to 15). We use put() method to insert the Key and Value pair in the HashMap. More than one node can share the same bucket. Each node has a data structure like a LinkedList.

Buckets: Array of the node is called buckets.

The bucket number is the address of the element inside the map.

The value received from the method is used as the bucket number. It returns the memory reference of the object in integer form. hashCode(): This is the method of the object class.If you override the equals() method, then it is mandatory to override the hashCode() method.

It compares the Key, whether they are equal or not. equals(): It checks the equality of two objects.There are four fields in HashMap.īefore understanding the internal working of HashMap, you must be aware of hashCode() and equals() method. It uses an array and LinkedList data structure internally for storing Key and Value. HashMap contains an array of the nodes, and the node is represented as a class. It stores the data in the pair of Key and Value. HashMap is a part of the Java collection framework. The integer value helps in indexing and faster searches. It is the process of converting an object into an integer value.