What is the difference between a Hashtable and a HashMap?

Though both Hashtable and HashMap are data-structure based upon hashing and implementation of Map interface, the main difference between them is that HashMap is not thread-safe but Hashtable is thread-safe. Another difference is HashMap allows one null key and null values but Hashtable doesn’t allow null key or values.

Is Threadsafe a Hashtable?

Yes Hashtable is thread safe, If a thread safe is not needed in your application then go through HashMap, In case, If a thread-safe implementation is desired,then it is recommended to use ConcurrentHashMap in place of Hashtable.

What is the difference between HashMap Hashtable and HashSet?

HashMap and Hashtable stores values in key-value pair. HashSet contains unique elements and HashMap, HashTable contains unique keys.

How is Hashtable synchronized?

Hashtable is synchronized. It ensures that no more than one thread can access the Hashtable at a given moment of time. The thread which works on Hashtable acquires a lock on it to make the other threads wait till its work gets completed. 2) HashMap allows one null key and any number of null values.

What is the difference between a Hashtable and Properties?

Properties is a very specialized class that’s designed to hold configuration and/or resources that are usually stored in some file. It has several features that Hashtable doesn’t have (and shouldn’t have): It supports reading and writing its content to a well-defined plain-text format (using load() / store() )

What is the difference between HashMap and tree Map?

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.

Is Hashtable a data structure?

In computing, a hash table (hash map) is a data structure that implements an associative array abstract data type, a structure that can map keys to values. A hash table uses a hash function to compute an index, also called a hash code, into an array of buckets or slots, from which the desired value can be found.

What is the difference between HashSet and set?

Set is the general interface to a set-like collection, while HashSet is a specific implementation of the Set interface (which uses hash codes, hence the name). Set is a parent interface of all set classes like TreeSet, LinkedHashSet etc. HashSet is a class implementing Set interface.

What is the relation between HashSet and HashMap choose the answer?

What is the relation between hashset and hashmap? Explanation: HashSet is implemented to provide uniqueness feature which is not provided by HashMap. This also reduces code duplication and provides the memory efficient behavior of HashMap.

Why HashMap is non synchronized?

HashMap is non-synchronized. It is not thread-safe and can’t be shared between many threads without proper synchronization code whereas Hashtable is synchronized. It is thread-safe and can be shared with many threads.

Is hash table a data structure?

Is hashtable thread safe in Java?

9 Answers. Yes Hashtable is thread safe, If a thread safe is not needed in your application then go through HashMap, In case, If a thread-safe implementation is desired,then it is recommended to use ConcurrentHashMap in place of Hashtable.

What happens when one thread does a put on another thread?

If one thread does a put, then another thread may see a stale value for the hashmap’s size. When a thread does a put that triggers a rebuild of the table, another thread may see transient or stale versions of the hashtable array reference, its size, its contents or the hash chains.

Should I use ConcurrentHashMap instead of hashtable?

If a thread-safe implementation is not needed, it is recommended to use HashMap in place of Hashtable. If a thread-safe highly-concurrent implementation is desired, then it is recommended to use ConcurrentHashMap in place of Hashtable. – Petar Minchev

What happens if I change the size of a hashmap?

If you change a HashMap in any way then your code is simply broken. He is correct. A HashMap that is updated without synchronization will break even if the threads are using disjoint sets of keys. Here are just some1 of the things that can go wrong. If one thread does a put, then another thread may see a stale value for the hashmap’s size.