custom hashmap in java

From: http://hi.baidu.com/calls911/blog/item/c0ed39da95379f3f33fa1c98.html 1. Memory occupied by the hashmap StructureUse the following methods to test the memory size occupied by the hashmap structure itself when storing 1 million key-value pairs: Hashmap hm1 = new hashmap For (INT I = 0; I Hm1.put (I, I );} In this

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

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

There are several options for applying HashMap in a Java multithreaded environment: using thread-safe java.util.Hashtable as an alternative Use the Java.util.Collections.synchronizedMap method to wrap an existing HashMap object as thread-safe. Using the Java.util.concurrent.ConcurrentHashMap class as an alternative, it has very good performance.And the above seve

, which is definitely longer than getting an element from an array.Memory consumption There is a good tool that can help us check the memory consumption of Java objects. Download the jar package from here: http://sizeof.sourceforge.net/Decompress the package and select sizeof. jar is copied to a directory, such as my/home/chenshu. Add this jar package to the project and set the JVM parameter-javaagent:/home/chenshu/sizeof. jar.This class library provi

Data Structure of HashMap and SparseArray in Java Recently, I heard from my colleagues that replacing HashMap with SparseArray can improve the performance, so we can perform a simple analysis on the data structures of these two classes. Data Structure of Hashmap Hashmap is a

1, HashMap initialization of literary writingHashMap is a commonly used data structure, usually used to do data dictionary or Hash lookup container. Ordinary youth would typically initialize this:hashmapMap.put ("name", "Test");Map.put ("Age", "20");After reading this code, many people will feel that this is too verbose, literary youth generally come:hashmap{Map.put ("name", "Test");Map.put ("Age", "20");}};It looks elegant, one step, one go's bright.

Java hashmap is very commonly used. This article studies its implementation algorithm, and finally hopes to calculate the quantitative data of memory usage and performance, and then draws a conclusion on when hashmap is used and when it cannot be abused.Hashmap is actually an array, and each element in the array is a linked list. When each element is put into a

Compared with HashMap in Java, the implementation of hash_map in C ++ STL is not perfect. The reason is that there are some small details:1. Hash Table growth mode: Hash_map: when the number of elements element_NUM exceeds the number of buckets bucket_NUM, determine the number of new buckets N. N is a prime number, which is selected from a prime number table. It must be greater than or equal to the number o

Java-15.7 Map (4)-Introduction to the working principle of HashMap-hash collision (often used as an interview) In this section, we will discuss hash collision. 1. What is hash collision? That is, the hashcode of the key of the two objects is the same. How can we get its value at this time? The answer is to traverse the Entry linked list at the position of the table through equals. 2. Example Normal example

ObjectiveTwo days ago in the company's internal blog to see a colleague to share the online services hanging off cpu100% article, let me think of hashmap in the improper use of the death cycle problem, here do a collation and summary, also by the way review under HashMap.Directly on the test code　　Depending on the machine configuration and performance, the number of threads and put quantities of the test results variespublic class Hashmapinfiniteloopt

is a key must implement the Hashcode and Equals methods. The hashcode and Equals methods inherit from the root class object, and if you use a custom class as a key, be very careful, as defined by the hash function, if two objects are the same, that is, Obj1.equals (OBJ2) =true, Their hashcode must be the same, but if two objects are different, their hashcode is not necessarily different, and if the hashcode of two different objects is the same, this