0
In computer science, a hash table, or a hash map, is a data structure that associates keys with values. The primary operation it supports efficiently is a lookup: given a key (e.g. a person's name), find the corresponding value (e.g. that person's telephone number). It works by transforming the key using a hash function into a hash, a number that is used as an index in an array to locate the desired location ("bucket") where the values should be. Hash tables support the efficient insertion of new entries, in expected O(1) time. The time spent in searching depends on the hash function and the load of the hash table; both insertion and search approach O(1) time with well chosen values and hashes.
Wiki User
∙ 15y ago
Wiki User
∙ 14y agoA Hashtable can be used just like any other Map in Java. You use it when you want to associate a set of keys with a set of values. It's kind of like how in an array you associate the index (the key) with some object (the value).
Methods of note:
// Add a new entry to the table which associates key with value.
put(K key, V value);
// Returns the value associated with key.
get(Object key)
// Returns the size number of keys in the hashtable.
size()
// Returns a Set of the keys in the hashtable.
keySet()
// Returns a Collection of the values in the hashtable.
values()
Add your answer:
Earn +20 pts
What is hash key?
hash key is an element in the hash table. it is the data that you will combine (mathematical) with hash function to produce the hash.
Advantage and distadvantage in hash table?
ANSWER A hash table is a way to find data in an array, when you have a known key and an unknown value that corresponds to the key. You use a hashing function on the key to create an index into the hash table containing the value. In the ideal case, this directly returns the corresponding value. In the usual case, a collision can occur. This means that the hashed key points to multiple possible values. A hash table is usually used on large arrays that would take a long time to search using other methods. A hash table can be very fast and use very little memory, and does not require the array to be sorted. The source code is slightly more complicated than some search methods. With a poorly designed hashing function when the hashed keys do not correspond one-to-one with the values, the secondary search after a hash collision can take a large amount of time.
What are the methods of hash table?
See the related link below for the Java API documentation for the Hashtable class and its methods.
What exactly does the hash tag symbol mean when used with words in between the?
The hash tag symbol is used to highlight or stress the words in use.
What difference does it make if you remove a period in a hash?
It makes a big difference because if you compared the hash: abcde.fg = hash 1 to abcdefg = hash 3 The results hash 1 and hash 3 are not equal.
What is hash key?
hash key is an element in the hash table. it is the data that you will combine (mathematical) with hash function to produce the hash.
What is hash table in sql?
temp table
What is the major advantage of a hash table?
The major advantage of a hash table is its speed. Because the hash function is to take a range of key values and transform them into index values in such a way that the key values are distributed randomly across all the indices of a hash table.
Advantage and distadvantage in hash table?
ANSWER A hash table is a way to find data in an array, when you have a known key and an unknown value that corresponds to the key. You use a hashing function on the key to create an index into the hash table containing the value. In the ideal case, this directly returns the corresponding value. In the usual case, a collision can occur. This means that the hashed key points to multiple possible values. A hash table is usually used on large arrays that would take a long time to search using other methods. A hash table can be very fast and use very little memory, and does not require the array to be sorted. The source code is slightly more complicated than some search methods. With a poorly designed hashing function when the hashed keys do not correspond one-to-one with the values, the secondary search after a hash collision can take a large amount of time.
What is the maximum number of entries that can be placed in the chained hash table?
There is no upper limit.
Insert value into hash table?
Insertion in hash tables is based on a 'key' value which is calculated on the basis of a hash function. This hash function generates the key based on what type of data it is fed. For example hash function for an integer input might look like this : int hash(int val) { return (val%101); } where return value of hash function would become a key. Complete implementation can be found at: http://simplestcodings.blogspot.com/2010/07/hash-table.html
Why hash are use?
4 narcosis.
Why do they call a pound sign hash tag?
why do people use hash sign in texting and facebook
What is the net collection class that allows an element to be accessed using a unique key?
Hash Table
What is hashing and its concepts in data structure?
Hashing allows us to map data of arbitrary length to data of fixed length. If we consider a table that contains thousands of objects, searching for a particular object could have a significant runtime cost if the objects require complex comparisons. Binary search would reduce that cost, however the cost of sorting the objects and then maintaining the order can be just as significant. Instead, we use a hash table. With a suitable hashing function, any object can be reduced to a single value. The range of output values is usually much smaller than the range of input values, thus two or more objects may well produce the same hash value. However, with an appropriate hash function, objects can be evenly distributed throughout the range of hash values. If we suppose that a single hash might be associated with up to n objects, then the size of the hash table will be up to n times smaller than the object table and can therefore be sorted and maintained n times more quickly than the object table. We then only need to sort n objects per hash to create an efficient hash lookup table. To search for an individual object, we pass the object through the hash function to obtain its hash and then search the hash table using a trivial binary search. If the hash exists (with a fixed-length table it is guaranteed to exist), we then use the more complex object comparisons to binary search the n objects associated with that hash value. The end result is that we narrow the search down to a much smaller subset of objects, thus significantly reducing the cost of searching. Hashing has other uses, particularly in cryptography. While it is possible to reverse engineer a hash value to produce n possible values for a given hash, cryptographic hashing is one-way only; we cannot use the hash to reproduce the input. Thus instead of storing passwords, we need only store the hashes produced by those passwords. Even knowing the precise implementation details of the hashing function won't help an attacker because in order to produce a particular hash value you'd still need to know which input actually produces it and that means testing each potential input individually. Doing it for just one input is hard enough, but doing it for two or more is nigh-on impossible (usernames, IP addresses, secret questions and answers and all other security information can also be hashed).
What else can one buy in an Amsterdam coffee shop?
Amsterdam coffee shops are famous for the sale of weed and hash. It is legal to buy and use weed or hash in coffee shops in Amsterdam but it is illegal to use or smoke weed or hash in public.
What are the methods of hash table?
See the related link below for the Java API documentation for the Hashtable class and its methods.
