hashmap implementation in java

HashMap the most basic implementation thought, as shown, uses the combination of array-linked lists to complete the storage of data. 　　　The position of the Entry in the array is determined by the hashcode of the key . To an array length of -, the load factor is0.75of theHashMapinserted inKeyof thehashcodeto be -,126,1,337,184, A, to,111the structure behind the object is:　　1%16 =1 ,337%16 =1. The last inser

allow null valueswhere key and value are objects and cannot contain duplicate keys, but can contain duplicate value.In Hashtable, both key and value do not allow null values.In HashMap, NULL can be used as a key with only one key, and one or more keys can have a value of NULL. When the Get () method returns a null value, the key may not be in HashMap, or the value corresponding to the key may be null. Ther

Recent code often appears in some cache caches to reduce the number of user requests resulting in high data server load, and these cache caches of the underlying implementation of the data structure support are map, and decided to look at the following map of the source code. So I started from HashMap. The Entry class source code in the map Entry HashMap used in

About Java Hashmap.entryset (), the document describes this: This method returns a set, which is a hashmap view, and the action on the map is reflected on the set, and vice versa. The original is Returns a Set view of the mappings contained in this map. The set is backed by the map, so changes to the map are reflected in the set, and Vice-versa. This article through the source code simple analysis This

write or write it.What's the difference with Java8 's hashmap?There are hash collisions, such as two hashes that fall on the same index after modulo, or two different keys that have the same hash value.JDK7 's practice is to build a linked list, and then insert the elements on top of each to perform the above judgment.And JDK8 in the chain table length reached 8, and the number of barrels reached 64, built a red black tree, to solve the serious confl

interface? List,set is map is notThe difference between ArrayList and vectors.I. Synchronization: vector is thread-safe, that is, synchronous, and ArrayList is a thread program is not secure, not synchronousTwo. Data growth: When growth is needed, vectors grow by default to the original, while ArrayList is half the originalThe difference between HashMap and HashtableI. Historical reasons: Hashtable is based on the old dictionary class,

carefully, Discover that Android is just optimizing the Hashcode () method in Java to make it easier to read, but the same principle is true =. =The specific code is compared as follows:Helpless, I can only continue to view the comparison in the source code, and finally found that the default constructor is different, in essence, the table size is not the same, Java table default size is 16*0.75=12 (capaci

expansion is time-consuming. static final int default_initial_capacity = 1 Below is a look at the general situation of the HashMap storage element: now look at the source analysis of the put operation: Now look at the source analysis of the get operation: In fact, the initial capacity and load factor of the HashMap can be changed through the hashmap of the

, void_ptr *outValue);/** * Free the hashmap */extern void hashmap_destroy(hmap_t in, hmap_callback_func fnFreeValue, void_ptr arg);/** * Get the current size of a hashmap */extern int hashmap_size(hmap_t in);#if defined(__cplusplus)}#endif#endif /* _HASHMAP_H_INCLUDED */ /** * hashmap.c * Generic hash map implementation. */#include "hashmap.h"#include /*** Ma

① Inherit differentpublic class Hashtable extends Dictionary implements maps public class HashMap extends Abstractmap implements mapThe methods in ②hashtable are synchronous, and the methods in HashMap are not synchronized by default.In the context of multi-threaded concurrency, you can use Hashtable directly, but to use hashmap, you need to increase the synchron

These days learned the bottom of the HashMap implementation, found about HASHMAP implementation of the blog is still a lot of, but almost all JDK1.6 version, and my JDK version is 1.8.0_25, in contrast, found HASHMAP implementation