custom hashmap in java

The implementation of a hash table-based Map interface. This implementation provides all the optional mapping operations and allows null values and null keys to be used. (in addition to not synchronizing and allowing Nulls, theHashMap class is roughly the same as Hashtable .) This class does not guarantee the order of the mappings, especially because it does not guarantee that the order is constant.This implementation assumes that the hash function distributes elements correctly between buckets,

Concept 1. hash The translation is a hash, and there is also a way to name hash. We should know what we have learned about the data structure. Hash is to use the hash algorithm to obtain a fixed-length output value of any length input value. The hash algorithm is not introduced here. Java hashmap Implementation 1. Storage Structure First, we know that the element stored in map is Entry. . The

number itself.So the hash () function will only readjust its value if it is greater than or equal to 216 for a non-null hash value.But what good is the adjustment?Let's first look at the put, the hash value is how to deal with (part of the source code):When looking for a bucket, this hash value is the zise-1 with the table above, the initial is 16, we take 16来 example.Think that the algorithm is HashValue Size-1, at this time size-1=15 binary is 1 1 1 1, that is, any like 16 binary 0x?0 (binar

Excellent articles for reference:The fourth edition of Java programming ideas"Effective Java" second EditionThe map interface is the structure of the map table , maintaining the corresponding relationship between the key object and the value object, called the key-value pair .> Hashcode () and Equals ()Hashcode () and Equals () are the identities used to identify objects.In a

Originalpublic class HashmapExtends abstractmapImplements Map1. Hash table based implementation of the Map interface. This implementation provides all of the optional map operations, and permits null values and the nul L Key. (The HashMap class is roughly equivalent to Hashtable, except that it's unsynchronized and permits null S.)2. This class makes no guarantees as to the order of the map; In particular, it does isn't guarantee that the order would

) {HashMapNewHashmap(); //Add a lot of entriesCountmap.put ("A", 10); Countmap.put ("B", 20); Valuecomparator VC=NewValuecomparator (COUNTMAP); TreeMapNewTreemap(VC); Sortedmap.putall (COUNTMAP); Printmap (SORTEDMAP); }}Although there are many ways to sort HashMap, the above approach is most respected in StackOverflow;Note: Using a comparator comparator to sort the treemap, the comparator compares key by removing the value of the key corresp

The collection HashMap in Java is also a collection that can be used to store data in each.The key value of elements in HashMap HashMap cannot be duplicated, that is, calling the Equals method to each other, and returning to false. The order of arrangement is not fixed.Common methods of

A detailed explanation of Java Hashmap,treemap and Linkedhashmap This morning when the interview asked Java,map related things, I remember the HashMap and TREEMAP related content, come back hurriedly tried a few demo understand Package Map; Import java.util.*; public class Hashmaps {public static void mai

Recently listening to colleagues said that the use of Sparsearray instead of HashMap can improve performance, so the edge of the two classes of data structure for a simple analysis.Data structure of HashMapHashMap is a combination of arrays and linked lists (in the data structure called "chain-Table hashing"), as shown in:Photo Source: Java's HashMap and HashtableData structure of SparsearraySparsearray ref

be found after the linked list, as for why the list is to save space, the list in memory is not continuous storage, So we can use memory more fully.Java's HashMapWhat does that have to do with the hashmap of our topic today? All right, do not square friends, into the subject. We know that the values in HashMap are all key,value, right, in fact, the storage here is very much like the above, the key will be

1 data structure of HASHMAP HashMap is actually an array of linked lists, the outermost is an array, and the elements of the array are linked lists. 2 HashMap's Put method: The source code is as follows: 3 source code is as follows HashMap get method: The source code is as follows: Analysis of 4 Concurrenthashmap: Mainly to divide the segment Resources:

Implementation of HashMap source code in a Java Collection1. Through the above article, we know that the underlying layer of HashSet is implemented by Map. What is Map? How is it implemented at the underlying layer? Next, let's analyze the source code to see the specific structure and implementation. The Map Collection class is used to store element pairs (called "keys" and "values"). Each key is mapped to

is the same, because HASHMAP cannot add duplicate keys. If the same, then overwrite, if not the same, then first determine whether it is TreeNode type:else if (p instanceof TreeNode) e = ((TreeNodethis, tab, hash, key, value);Here is not now turned red black tree (in the case of a large number of hash conflicts, the list will turn red black tree), generally our small data in the case, is not to turn, so here for the moment not to consider this sit

Before JDK8, you can use keyset or entryset to traverse HASHMAP,JDK8 by introducing Map.foreach for traversal. Keyset is actually traversed 2 times, one is to iterator object, and the other is to remove key from the HashMap corresponding value. And EntrySet just iterates over it and puts both the key and the value in the entry, which is more efficient. If it is JDK8, use the Map.foreach method. 1. Basic usa

There are two ways to HashMap traversal in Java:The first type:map map = new HashMap ();Iterator iter = Map.entryset (). Iterator ();While (Iter.hasnext ()) {map.entry Entry = (map.entry) iter.next ();Object key = Entry.getkey ();Object val = Entry.getvalue ();}The efficiency is high, must use this kind of way later! The second type:map map = new HashMap ();Itera

Fibonacci is the first item of 0, the second item is 1, and each subsequent item is a sequence of two items in front.Source: Fibonacci.javapublic class Fibonacci{private static int times=0, public static void Main (String args[]) { int nums = Fibonacci (+); SYSTEM.OUT.PRINTLN ("Result:" +nums); System.out.println ("Number of times:" +times); } static int fibonacci (int n) {times++;if (nFor the 30th term. Called function 2,692,539 times, efficiency and lowThe second optimization algorith

(type)! =-1) {A.add (key);}}} catch (Exception ex) {} finally {return A;}}}3. Call@OverridePublic Dcjqrfbview Getmap (string qlinkid, String country, string online, String devtype, String devtype1, String beautify, String adminqlinkid) throws Exception {Dcjqrfbview viewrespons=new Dcjqrfbview ();String cache_key=new StringBuilder (). Append (Qlinkid). Append (Country). Append (online). Append (Devtype). Append ( DEVTYPE1). Append (Beautify). Append (Adminqlinkid). toString ();cacheif (c!=null!c

/* Review: As long as the underlying data structure is a collection of hash tables, overwrite the two methods to guarantee the uniqueness of the elements in the hash table. public int Hashcode () public boolean equals (Object obj) (1) HashMap guarantees the uniqueness of the element, does not repeat, (principle: Overrides the Hashcode () and Equals () methods in the object class), The object class can implement the comparable interface and implement t

")); - - //Create a third collection element inHashmapNewHashmap(); - to //add elements to this collection +Hm3.put ("Make Fox Chong", "Ren Ying"); -Hm3.put ("林平", "Keilingshan"); the * //Add the above 3 small collections to the total collection $ List.add (HM1);Panax Notoginseng List.add (HM2); - List.add (HM3); the + //traversal of the total collection A for(hashmaplistkey:list) { the //iterate over subset

the student's information, y means continue, n means exit"); } System.out.println ("The Student information entered is:"); System.out.println ("Number of Students:" +list.size ()); IteratorList.iterator (); inti = 1; while(It.hasnext ()) {HashMapIt.next (); System.out.print ("First" + i + "Student's information"); System.out.println ("Study Number:" + stumap.get ("Studentno") + ", Name:" + stumap.get ("name") + ", Age:" + Stumap.get ("ages"))); } }}Original: http://blog.csdn.net/woshisap/ar