Thereafter, we are getting the size, retrieving the value, and checking for the presence of the key in the HashSet. In this example, we are adding values to the HashSet. So, if multiple threads access a hash set concurrently, and at least one of the threads modifies the set, it must be synchronized externally. Moreover, this implementation is not synchronized. The class does not guarantee the constant order of elements over time. The HashSet class of java.util package implements the Set interface, backed by a hash table which is actually a HashMap instance. Here, we will demonstrate the operations on HashSet class. ("value for key Electrical is "+h.get("Electrical")) ĪLSO READ: If Else Java Statement Explained Example 3 : Operations on HashSet ("Does hashmap contains computer? "+h.containsKey("computer")) ("Does hashmap contains Computer? "+h.containsKey("Computer")) ("After updating the value and adding duplicate keys: ") Program to demonstrate HashMap vs Hashtable vs HashSet ![]() Thereafter, we are getting the size, retrieving the value, and checking for the presence of the key in the hashmap. In this example, we are adding some key value pair to the hashmap. So, this is faster as compared to the Hashtable. The HashMap is asynchronized implementation of hashing. It stores the data in (Key, Value) pairs, and we can access them by an index of another type. It provides the basic implementation of the Map interface of Java. Here, we will demonstrate the operations on HashMap. Some examples to demonstrate the comparison Example 1 : Operations on HashMap The add() method is used to insert the elements in HashSet.ĪLSO READ: How to Compare Characters in Java The put() method is used for inserting values. We can traverse HashSet using the iterator. We can traverse Hashtable using enumerator and iterator both. We can traverse HashMap using the iterator. It allows one null key and multiple null values It does not allow duplicate keys but duplicate values are allowed. It is a hash table based implementation of Set interface. This class implements a hash table, which maps keys to values. HashMap was created later.It is a hash table based implementation of Map interface. HashMap is an advanced version and improvement on the Hashtable. Since null is not an object, it can’t implement these methods. In order to successfully store and retrieve objects from a HashTable, the objects used as keys must implement the hashCode method and the equals method. Now you must be wondering why HashTable doesn’t allow null and HashMap do? Otherwise, we will get a null pointer exception. Null is not allowed for both key and value. It increases the waiting time of the thread and hence performance is low. Threads are not required to wait and hence relatively performance is high. Multiple threads can operate simultaneously and hence hashmap’s object is not thread-safe.Īt a time only one thread is allowed to operate the Hashtable’s object. HashMap is generally preferred over HashTable if thread synchronization is not needed.ĭifference Between Hashmap and Hashtable S.HashMap allows one null key and multiple null values whereas Hashtable doesn’t allow any null key or value.It is thread-safe and can be shared with many threads. It is not thread-safe and can’t be shared between many threads without proper synchronization code whereas Hashtable is synchronized. If you do, use a ConcurrentHashMap (thanks, akappa). ![]() Slightly OT: If you don't need the synchronization, use HashMap instead of Hashtable.
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