Map of the Java Collection framework

Show Me the code!

Commonly used map has treemap,hashmap,hashtable,linkhashmap, the following code on the above four are compared and simple description of its underlying implementation.

 Public classMyMap { Public Static voidTestaddtreemap () {TreeMap<String,Object> TreeMap =NewTreemap<string, object>(); Treemap.put ("Zhao Yun", 23); Treemap.put ("Caocao", 24); Treemap.put ("Ma Chao", 25); Treemap.put ("Sima Yi", 26); Treemap.put ("2", 0); Treemap.put ("1", 0); Treemap.put ("3",NULL);  for(Map.entry<string, object>Entry:treeMap.entrySet ()) {System.out.println (Entry.getkey ()+ ": " +Entry.getvalue ()); }    }     Public Static voidTesthashmap () {Map<string, object> HashMap =NewHashmap<string, object>(); Hashmap.put ("Zhao Yun", 23); Hashmap.put ("Caocao", 24); Hashmap.put ("Ma Chao", 25); Hashmap.put ("Sima Yi", 26); Hashmap.put (NULL,NULL);  for(Map.entry<string, object>Entry:hashMap.entrySet ()) {System.out.println (Entry.getkey ()+ ": " +Entry.getvalue ()); }    }     Public Static voidTestlinkedhashmap () {Linkedhashmap<String,Object> Linkedhashmap =NewLinkedhashmap<string, object>(); Linkedhashmap.put ("Zhao Yun", 23); Linkedhashmap.put ("Caocao", 24); Linkedhashmap.put ("Ma Chao", 25); Linkedhashmap.put ("Sima Yi", 26); Linkedhashmap.put (NULL,NULL); Linkedhashmap.put ("2", 1); Linkedhashmap.put ("1", 1);  for(Map.entry<string, object>Entry:linkedHashMap.entrySet ()) {System.out.println (Entry.getkey ()+ ": " +Entry.getvalue ()); }    }     Public Static     voidtesthashtable () {Hashtable<String,Object> hashtable =NewHashtable<string, object>(); Hashtable.put ("Zhao Yun", 23); Hashtable.put ("Caocao", 24); Hashtable.put ("Ma Chao", 25); Hashtable.put ("Sima Yi", 26);//Hashtable.put (null,null);         for(Map.entry<string, object>Entry:hashtable.entrySet ()) {System.out.println (Entry.getkey ()+ ": " +Entry.getvalue ()); }    }     Public Static voidMain (string[] args) { System.out.println ( "--hashmap--: Features: unordered, non-thread safe, parent: abstractmap-allow null Key/value"); Mymap.testhashmap (); //Bottom-level implementation: is a hash table (array with single-linked list implementation), with hashcode positioning to deposit a storage space
       System.out.println ("--hashtable--Features: unordered, thread safe, parent class dirtory, disallow null Key/value"); Mymap.testhashtable (); //The underlying implementation is consistent with HashMap just adding synchronized to all methods
System.out.println ("-linkhashmap--Features: Orderly!" ( The order here is not meant to be sorted! Instead, it is returned in the order in which it was inserted) non-thread safe, the parent class HashMap allow null Key/value "); Mymap.testlinkedhashmap ();//consistent with the implementation of HashMap, the only difference is the use of a two-way loop linked list, adding before pointers, so you can easily find the previous node to achieve an orderly
     System.out.println ("--treemap--Features: Key value ordered non-thread safe parent class: Abstractmap allows value to be null key is forbidden to null"); Mymap.testaddtreemap ();//The bottom-level implementation is a balanced binary tree (red-black tree) to sort the key if you need key to be ordered to use, here TreeMap set a 2 and 1 key results show that the key is sorted    }}

HASHMAP underlying data structure display diagram

HashMap is a combination of an array and a single linked list, while the Linkhashmap is roughly the same as the above, but the only difference is that he uses a doubly-linked list so there's a before in addition to next so you can find the previous element in order.

Map of the Java Collection framework