custom hashmap in java

HashMap key and value values are strong references, meaning that the HashMap object is not destroyed when the key value pair is not destroyed, but Weakhashmap, when the inside of the key value is not destroyed when the words may be automatically destroyed by the Java recycling mechanismWeakhashmap whm=new weakhashmapWhm.put (New String ("PHP"), "75 Yuan");Whm.put

From the source code analysis java Collection [HashMap], the source code javahashmap As we know, Map stores key-value pairs. Its basic unit is to implement Node static class Node You can see its function by looking at the definition. It stores an object next to the next node. Therefore, we can probably think of its storage method stored by the linked list. In fact, by reading the information, we can also

HashMap is one of the most frequently-used and important data structures. It provides dictionary operations, and the efficiency of Insert, Search, and Delete operations is high. This article will try to use Java to implement a simplest HashMap. Because of its simplicity, it is easy to see the true design idea of HashMap.What is Hash? In my understanding, Hash is

is necessary to implement the Containsvalue in map:publicbooleanreturn contains ( value);} There's no difference in performance, so it's misleading to think that contains is a key that determines if there is an associationDefault value size comparisonThe default size of the hash array in Hashtable is 11, and the increment is old*2+1. The default size of the hash array in HashMap is 16, and must be a 2 indexHashtable Public Hashtable () {

Analysis of Java HashMap Traversal In the original memory, Java HashMap traversal is nothing more than for each or iterator. However, the performance, advantages and disadvantages of traversal are general and unknown. For such basic problems, for Wang Er (Java programming fo

1: Even a map interface is implemented, the underlying data structure is the same, both are transient decorated entry array, transient modified variables will not be serialized is not persisted, the process of serialization will not include this variable, The lifetime of this variable is simply not persisted to the memory disk during the user's call. This facilitates the preservation of some sensitive information2:hashmap is insecure, cannot be synchr

!"); } keysettest (HASHMAP); Entrysettest (HASHMAP); } Static voidkeysettest (map map) {LongStartTime =calendar.getinstance (). Gettimeinmillis (); Iterator ITER=Map.keyset (). iterator (); while(Iter.hasnext ()) {System.out.print (Map.get (Iter.next ())); } LongEndTime =calendar.getinstance (). Gettimeinmillis (); System.out.println ("\nkeysettest:" + (Endtime-starttime));//Ms }

out and the operation, actually with the previous capacity of the index of 8 o'clock is changed to 1000 and the bit, the capacity is enlarged to twice times before, can be seen as the addition of a container as large as the previous container. It is obvious that the index values are small and placed in front of the container, and placed large behind. So we only need to calculate the hash and the value of the previous capacity and the result of the operation is 1, we can know whether the origina

Conversion] Two Methods of hashmap traversal in Java: http://www.javaweb.cc/language/java/032291.shtmlfirst: 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 ();} i

The video introduces the content of HashMap through the following four aspectsFirst, what is HashMapA hash hash converts an arbitrary length into a fixed value by an algorithm (the hash function algorithm). Map: x, y Storage Summary: The value of the hash, then the value to the map, then the value stored in the map of the hashmap rationale1. Can the KEY be empty? Yes, null as a key to store2, if the hash ke

(i) Hashing algorithmA hashing algorithm that maps raw data through a hash function to a shorter fixed-length binary value, referred to as a hash value.There are two basic features of the hash algorithm: repeatable and irreversible. Theoretically computed hashes are repeatable, but a good hash function basically does not happen. cannot be reversed, knowing that the hash value cannot be inferred from the original data.Hashing algorithms are typically used for quick lookups (such as

[Simple Java] commonly used HashMap method, simplejavahashmap HashMap is very useful when you need to count elements. For example, count the number of times each character appears in a string: package simplejava;import java.util.HashMap;import java.util.Map.Entry;public class Q12 { public static void main(String[] args) {

= = null) {if (other.name! = null) return false; } else if (!name.equals (Other.name)) return false; return true; }/* (non-javadoc) * @see java.lang.object#tostring () */@Override public String toString () {Retu RN "Person [name=" + NAme + ", age=" + Age + "]"; }}Why? The output maps appear with the same key.The preliminary judgment is related to the hashcode mechanism of HASHMAP, which detects the hash value of the element key only when th

algorithm ideas are as follows:A. Find the corresponding box according to the hashB. Locate the object in the box that you want to delete. Depending on the storage structure of the elements in the box (list or tree), different search methods are used.C. After finding the object to be deleted, the call takes a different node deletion policy depending on the storage structure.The HASHMAP data structure relationship is simple, as follows.KeySet (), valu

() ... {Java.util.HashMap HashMap =NewJava.util.HashMap (); for(inti = 0; i LongBS = Calendar.getinstance (). Gettimeinmillis (); Java.util.Iterator it = Hashmap.entryset (). Iterator (); while(It.hasnext ()) ... {Java.util.Map.Entry Entry = (java.util.Map.Entry) it.next ();//Entry.getkey () returns the key corresponding to this key//Entry.getvalue () returns the value corresponding to this keySystem.out.print (Entry.getvalue ());　　} System.out.print

 In a nutshell: The big difference between the two is that HASHMAP does not guarantee the order of the data put in, while Linkedhashmap guarantees the order of the data put in. In other words, the order in which the data is added HashMap and the order in which the data is traversed is not necessarily, while linkedhashmap guarantees what the data order is when it is added and what the data order is in the

: Pointers require additional space, so when the node size is small, open addressing method is more space-saving, and if the saving of the pointer space to expand the scale of the hash table, can make the filling factor smaller, which reduces the open addressing method of conflict, thus improving the average search speed Why is hashmap in java1.8 with red and black trees?After the jdk1.8 version, Jav