What is the capacity of a Hashtable?
Constructs a new, empty hashtable with a default initial capacity (11) and load factor (0.75).
What is difference between Hashtable and HashMap?
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. HashMap allows one null key and multiple null values whereas Hashtable doesn’t allow any null key or value.
Is Hashtable deprecated?
Ans. HashTable has been deprecated. Moreover, there is already a raw type HashMap. The only difference between the HashTable and HashMap is that Hashtable is synchronized whereas HashMap is not.
What is the time complexity of a Hashtable?
Like arrays, hash tables provide constant-time O(1) lookup on average, regardless of the number of items in the table. The (hopefully rare) worst-case lookup time in most hash table schemes is O(n).
What is size of hash?
But a good general “rule of thumb” is: The hash table should be an array with length about 1.3 times the maximum number of keys that will actually be in the table, and. Size of hash table array should be a prime number.
Should I use Hashtable or HashMap?
HashMap should be preferred over Hashtable for the non-threaded applications. In simple words , use HashMap in unsynchronized or single threaded applications . We should avoid using Hashtable, as the class is now obsolete in latest Jdk 1.8 . Oracle has provided a better replacement of Hashtable named ConcurrentHashMap.
What is the time for hash insertions?
| Hash table | |
|---|---|
| Type | Unordered associative array |
| Invented | 1953 |
| Time complexity in big O notation | |
| Algorithm Average Worst case Space O(n) O(n) Search O(1) O(n) Insert O(1) O(n) Delete O(1) O(n) |
What is hash in Java?
Hashing is the process of mapping the data to some representative integer value using the concept of hashing algorithms. In Java, a hash code is an integer value that is linked with each object. Hashing finds its data structure implementation in HashTables and HashMaps.
What to use in place of hashtable in Java?
Unlike the new collection implementations, Hashtable is synchronized. 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.
How to store and retrieve objects from a hashtable?
To successfully store and retrieve objects from a hashtable, the objects used as keys must implement the hashCode method and the equals method. An instance of Hashtable has two parameters that affect its performance: initial capacity and load factor.
Why is the hash table open in Java?
Note that the hash table is open: in the case of a “hash collision”, a single bucket stores multiple entries, which must be searched sequentially. The load factoris a measure of how full the hash table is allowed to get before its capacity is automatically increased.
What is the default load factor for a hashtable?
Constructs a new hashtable with the same mappings as the given Map. The hashtable is created with an initial capacity sufficient to hold the mappings in the given Map and a default load factor (0.75). t – the map whose mappings are to be placed in this map. NullPointerException – if the specified map is null.