java hashmap example

The important nature and optimization of HashMap in java, javahashmap Preface As HashMap plays an important role in java Development, it is particularly important to summarize some important attributes and optimization points of hashmap, at the same time, it can also improve

are important parameters that affect the performance of the HashMap, where capacity represents the number of buckets in the hash table, the initial capacity is the capacity to create a hashtable, and the load factor is the size of the hash table before its capacity is automatically increased by a scale, which measures how much space is used for a hash list, The larger the load factor, the higher the filling of the hash table, and the smaller the inve

Entry[newCapacity]; //将原有数组转到新的数组中 transfer(newTable); table = newTable; //重新设置阈值，为新的容量和负载因子的乘积 threshold = (int)(newCapacity * loadFactory);}Where the array migration logic is mainly implemented in the transfer () function, the function is implemented and annotated as follows:voidTransfer (entry[] newtable) {entry[] src = table;intnewcapacity = Newtable.length;//Iterate through all the table entries in the array for(intj =0; J //When the table item index has a value exists,

The HashMap is a very common, widely used type of data. This article through the example code to introduce the relevant knowledge of JS HashMap, the specific code content as follows: /** * Map object, realize map function * Interface: * Size () Get the number of map elements * IsEmpty () to determine whether the map is empty * Clear () Delete all elements

This article hashmap the realization of the source code for a simple analysis. The version information of the HashMap source used is as follows:/* * @ (#) Hashmap.java 1.73 07/03/13** Copyright 2006 Sun Microsystems, Inc. All rights reserved.* SUN proprietary/confidential. Use are subject to license terms. */I. OverviewEach object in Java has a hash code, which c

same key, and each key can only map one value. The map interface provides three sets of views. The map content can be treated as a set of keys, a set of values, or a set of key-value ing.Hashmap classHashmap is similar to hashtable. The difference is that hashmap is non-synchronous and allows null, that is, null value and null key ., However, when hashmap is treated as a collection (the values () method ca

follows: The relevant code is as follows: By default, the traversal mode of LINKEDHASHMAP is insert mode, and if you want to explicitly specify a get read mode, set the parameter of//its constructor to true, (false means insert mode) Linkedhashmap Linkedhashmap = new Linkedhashmap ((float) 0.75,true); Linkedhashmap.put ("Name", "Louis"); Linkedhashmap.put ("Age", "the"); Linkedhashmap.put ("Sex", "male"); Linkedhashmap.get ("name");//g

in synchronized block...Synchronized (m) {// Synchronizing on m, not s!Iterator I = s. iterator (); // Must be in synchronized blockWhile (I. hasNext ())Foo (I. next ());} 3. In HashMap, null can be used as a key, and there is only one such key. One or more keys can correspond to null values. When the get () method returns a null value, it can indicate that the key does not exist in HashMap or that the cor

: If a Thread-safe implementation is not needed, it's recommended to use HASHMAP in place of Hashtable. If a thread-safe highly-concurrent implementation is desired and then it's recommended to use Java.util.concurrent.Concurren Thashmap in place of Hashtable. Simply put, if you don't need thread safety, then use HASHMAP, if you need thread safety, then use Concurrenthashmap. Hashtable has bee

Turn from: http://www.cnblogs.com/fczjuever/archive/2013/04/07/3005997.html 1. Elaborates In the Java map Traversal way, many articles are recommended to use EntrySet, think it is more efficient than keyset. The reason: The EntrySet method gets all the keys and value sets at a time, and keyset gets only a set of keys, which, for each key, goes to the map to find an extra value, which reduces overall efficiency. So what is the situation? To understand

] View plaincopypublic class Test2 {public static void Main (String args[]) {StringBuilder s = new StringBuilder ("Hello");System.out.println (s);Foo (s);System.out.println (s);}public static void Foo (StringBuilder s) {s = new StringBuilder ("World");}}What about this time? Will you output "Hello" and then output "world"? No, it's still two times "Hello".Suffice to say that this problem is not related to the immutable characteristic of string. Whether it's a immutable type or a generic type, th

A: Knowledge supplement (this HashMap map and C + + map is still a big difference, the difference between the big people jaw-dropping, of course, the role of the two is consistent, but the function name is very large, even iterator difference is very large)(1) difference between HashMap and Hashtable (only map wood in C + + is HashMap)