java hashmap example

It seems that map inherits from Collection like other Collection classes. In fact, Map and Collection do not have any relationship at the structural level, by viewing the source code, we can find that all map operations are based on key-value pairs, rather than individual elements. The following uses HashMap as an example to gain an in-depth understanding of the implementation mechanism of Map. In this proc

Differences between Map and HashMap, Hashtable, and HashSet in Java, hashmaphashsetHashMap and Hashtable both implement the Map interface, both save the K-V pair (key-value Pair); HashSet implements the Set interface, the nature is similar to the Set. Differences between HashTable and HashMap1. Different Hashtable inherited from the Dictionary class and HashMap

write or write it.What's the difference with Java8 's hashmap?There are hash collisions, such as two hashes that fall on the same index after modulo, or two different keys that have the same hash value.JDK7 's practice is to build a linked list, and then insert the elements on top of each to perform the above judgment.And JDK8 in the chain table length reached 8, and the number of barrels reached 64, built a red black tree, to solve the serious confl

Cause Today in the project encountered a very "wonderful" problem. This is roughly the case: Android Terminals and servers (Spring), exactly the same string key values in the HashMap into the order is not the same, which directly led to the server and the Android terminal using the HMACSHA256 algorithm to encrypt the digest is not the same, The server will not be able to perform proper data validation. Then with depressed mood to the program plus br

, Hashtable also uses the enumeration approach in detail:Map map = new HashMap (), Map.put ("A", "N"), Map.put ("B", "n"), Map.put ("C", "N"); Iterator iter = Map.entryset (). Iterator (); while (Iter.hasnext ()) { Map.entry Entry = (map.entry) iter.next (); Object key = Entry.getkey (); Object val = Entry.getvalue ();} or for (Map.entry Entry:map.entrySet ()) { Object key = Entry.getkey (); Object value = Entry.getvalue ();}Why do

, value, I); // Add new elements, key!Return NULL; // return without the same key value} The key methods are analyzed as follows: Void addentry (INT hash, object key, object value, int bucketindex ){Table [bucketindex] = new entry (hash, key, value, table [bucketindex]); Because the hash algorithm may make different key values have the same hash code and have the same table index, for example: the hash values of key = "33" and key

This article reproduced others, the original address: http://www.xyczero.com/blog/article/16/CauseToday in the project encountered a very "wonderful" problem. This is basically the case: Android terminal and Server (Spring), the exact same string key value to put in the HashMap in order, which directly led to the server and Android terminal with the HmacSHA256 algorithm encryption of the digest is not the same, The server will not be able to verify th

① Inherit differentpublic class Hashtable extends Dictionary implements maps public class HashMap extends Abstractmap implements mapThe methods in ②hashtable are synchronous, and the methods in HashMap are not synchronized by default.In the context of multi-threaded concurrency, you can use Hashtable directly, but to use hashmap, you need to increase the synchron

Hash calculation is the element in which the computing element should be placed in the array. It is accurate to the linked list to which it is placed. According to Java rules, if you want to put an object into hashmap, your object class must provide the hashcode method and return an integer. For example, the string class has the following method: [

to synchronize No isK,v can null whetherHashMap is a lightweight implementation of Hashtable (non-thread-safe implementation), they all complete the map interface,The main difference is that HASHMAP allows null (NULL) key values (key), which may be more efficient than Hashtable due to non-thread safety.HashMap allows NULL to be used as a entry key or value, and Hashtable is not allowed.HashMap hashtable contains method removed, changed to Containsval

.Hashtable supports iterator and enumeration two ways of traversing . 5) Different initial capacity and expansion modethe default capacity of the HashMap is twice times the capacity of the original, when expanding;the default capacity of the Hashtable is one, and the capacity is changed to twice timesthe original +1.6) The hash value algorithm for adding key-value is differentHashMap When adding elements, a custom hashing algorithm is used ;Hashtable

HashMap is a lightweight implementation of Hashtable (non-thread-safe implementation), they all complete the map interface, the main difference is that the HASHMAP allows null (NULL) key value (key), because of non-thread security, the efficiency may be higher than Hashtable.HashMap allows NULL to be used as a entry key or value, and Hashtable is not allowed.HashMap hashtable contains method removed, change

The analysis of a storage class is nothing more than two points: the data structure used for storage and the operating mechanism of storage. Data structure: Array [Java]/*** The table, resized as necessary. Length MUST Always be a power of two.*/Transient Entry [] table; /*** The table, resized as necessary. Length MUST Always be a power of two.*/Transient Entry [] table;Entry Linked List format. That is, HashMap