java hashmap example

Java learning, see Hashmap,hashset class, in line with not only to stay on the level (many companies interview to ask the bottom), learn the JDK source code, record notes.Source code from jdk1.7 under the Src.zipHashMap is a type of key-value pair that provides a key-value data structure that implements the map interface, where the value of key is unique, that is, a key can only be mapped to a unique value

HashMap inHashTableThere are basically three improvements on: * The Map interface is installed, rather than the Dictionary of JDK. The Map interface is richer and more reasonable. * The null key and null value are acceptable. * The synchronization speed is greatly improved (ConcurrentHashMap is used for synchronization, with several improvements: Segment locks, immutability, Unsafe CAS operations, and weak consistent iterators ). if (key == nu

Hashtable classHashtable inherits the map interface and implements a hash table of key-value mappings. Any object that is Non-null (non-null) can be a key or value. Adding data using put (Key,value), fetching data using get (key), the time cost of these two basic operations is constant.Hashtable adjusts performance by initial capacity and load factor two parameters. Typically, the default load factor 0.75 achieves a better balance of time and space. Increasing the load factor saves space but th

element problem. This time we take the 3, 5, 7 order to demonstrate:1, if the thread one executes to the 9th line of code is suspended by CPU scheduling:2, thread two execution completion:3, this time then the execution line Cheng, first place 7 this entry:4, then place 5 This entry:5, because the next of 5 is null, at this time the expansion action ends, resulting in 3 of this entry lost.OtherThe problem was reported to Sun, but Sun did not think it was a problem. Because

Today we continue to look at the source code of HashMap, several common methods for analysis. Before we analyze, we must first understand the structure of HashMap. See before I analyzed the ArrayList and LinkedList source of friends should be clear, ArrayList internal is an array to achieve, linkedlist inside is linked to the list. And HashMap is a combination of

HashMap is a lightweight implementation of Hashtable (non-thread-safe implementation), they all complete the map interface, mainly different from the hashmap allow null (NULL) key value (key), because of thread safety, more efficient than Hashtable.HashMap allows NULL to be used as a entry key or value, and Hashtable is not allowed. HashMap Hashtable's contains (

Java HashMap and javahashmapPerformance Factor of HashMap 1. Capacity: The number of buckets. 2. Initial Capacity: the number of bits in a table created. If you know how many items will be stored in the HashMap, creating a HashMap with an appropriate initial capacity will

[] args) {MapNewHashmap(); //add elements to the container: store them as key-value pairs.Map.put ("Jack","Jackie Chan"); Map.put ("Jay","Jay Chou"); Map.put ("Eason","Eason Chan");//adding elementsMap.put ("Jack","Jack");//if the key repeats, the overwrite will occurSystem. out. println (map); //Method 1: Get the collection of keys first, get the value by keySetMap.keyset (); for(String key:keyset) {String value= map.Get(key); System. out. println (key+"----"+value); } System. out. println ("-

If anyone asked me to describe HashMap's working mechanism, I would simply answer: "Hash based rules." This sentence is very simple, but to understand this sentence, first we have to understand what is a hash, is not it? What is a hasha hash is simply a unique string that is obtained by applying an algorithm to a variable/object attribute, using this string to determine the uniqueness of the variable/object. A correct hash function must adhere to this guideline. When a hash function is applied

")); * //Containsvalue (Object value): Whether the value is inclusive $System.out.println ("contains value 0:" + map.containsvalue (NewInteger (0)));Panax Notoginseng //Remove (Object key): Key value pair corresponding to key key -Map.Remove ("three"); theSystem.out.println ("Delete three"); +SYSTEM.OUT.PRINTLN ("Map:" +map); A //Clear (): Empty HashMap the map.clear (); +System.out.println ("Empty