What is the difference between HashMap vs Hashtable?
One of the major differences between HashMap and Hashtable is that HashMap is non-synchronized whereas Hashtable is synchronized, which means Hashtable is thread-safe and can be shared between multiple threads but HashMap can not be shared between multiple threads without proper synchronization.
What is HashMap explain in interview?
1. Explain the internal working of a HashMap. A hashmap uses a hashtable but what many people don’t know is that it is internally created using two data structures namely an array and a linked list. Whenever you declare a hashmap what is going to happen internally is that it will create an array of buckets.
Is Hashtable faster than HashMap?
HashMap is not synchronized, therefore it’s faster and uses less memory than Hashtable. Generally, unsynchronized objects are faster than synchronized ones in a single threaded application.
Why is a hash better than a map?
Thread synchronization : Map is generally preferred over hash table if thread synchronization is not needed. Hash table is synchronized. Thread safe: STL Maps are not thread safe whereas Hashmaps are thread safe and can be shared with many threads.
Why HashMap is fast?
The reason that HashMap is faster than HashSet is that the HashMap uses the unique keys to access the values. It stores each value with a corresponding key and we can retrieve these values faster using keys during iteration. While HashSet is completely based on objects and therefore retrieval of values is slower.
Why is HashMap useful?
Hashmaps are probably the most commonly used implementation of the concept of a map. They allow arbitrary objects to be associated with other arbitrary objects. This can be very useful for doing things like grouping or joining data together by some common attribute.
Can you store a duplicate key in HashMap?
Implementation: HashMap implements Map interface and HashSet implements Set interface. Duplicates: HashSet doesn’t allow duplicate values. 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.
Why is Hashtable slow?
Hashtable is slow due to added synchronization. HashMap is traversed by Iterator. Hashtable is traversed by Enumerator and Iterator. Iterator in HashMap is fail-fast.
What are the advantages of HashMap?
Advantages of HashMap
- Allows insertion of key value pair.
- HashMap is non synchronized. HashMap cannot be shared between multiple threads without proper synchronization.
- HashMap is a fail-fast iterator.
- Faster access of elements due to hashing technology.
Why are HashMap keys immutable?
Make HashMap key object immutable For above basic reasoning, key objects are suggested to be IMMUTABLE. Immutability allows you to get same hash code every time, for a key object. So it actually solves most of the problems in one go. Also, this class must honor the hashCode() and equals() methods contract.
Why shouldn’t you use a hash table?
There are some operations which are not efficiently supported by hash tables, such as iterating over all the elements whose keys are within a certain range, finding the element with the largest key or smallest key, and so on. The O(n) complexity is on average.
Is hash table the best data structure?
The most valuable aspect of a hash table over other abstract data structures is its speed to perform insertion, deletion, and search operations. Hash tables can do them all in constant time. For those unfamiliar with time complexity (big O notation), constant time is the fastest possible time complexity.
Can we put null as key in HashMap?
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 is the difference between Hashtable and HashMap in Java?
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. This means you cannot use HashMap in a multi-threaded Java application without external synchronization.
When to use hashtable instead of enumeration in Java?
Also, in a Hashtable, enumeration is not fail-safe. So if you need to be able to change the content of the structure while enumerating, a Hashtable would be more appropriate. Thanks for contributing an answer to Stack Overflow!
Can hashtable be used to implement map?
Sure, Hashtable has been retrofitted to implement Map but that’s not terribly useful. It has the main problem in that it’s synchronized. This means that it will be slow in any circumstance where it is shared between threads. ConcurrentHashMap is a better choice in that situation.
How do you hash a value in a hashtable?
When using a Hashtable or HashMap, we specify an object that is used as a key and the value that you want to be linked to that key. The key is then hashed, and the resulting hash code is used as the index at which the value is stored within the table.