Java: Container/Collection (Map (HASHMAP,TREEMAP))

HASHMAP:

*map Interface: Store data in a way that is a key-value pair. Disordered
* Common Implementation classes:
*--hashmap: The implementation of a hash table-based MAP interface.
* Common methods of construction:
*hashmap () constructs an empty HashMap with the default initial capacity (16) and the default load factor (0.75).
*hashmap (int initialcapacity) constructs an empty HashMap with the specified initial capacity and default load factor (0.75)
* Common methods:
*put (K key, V value) associates the specified value with the specified key in this mapping.
* Get (Object key) returns the value mapped by the specified key, or null if the map does not contain any mapping relationships for that key.
* Size () returns the number of key-value mapping relationships in this map.
* Remove (Object key) Removes the mapping relationship for the specified key from this mapping, if any.
* Clear () Removes all mapping relationships from this mapping.
* ContainsKey (Object key) returns True if this map contains a mapping relationship for the specified key.
* Containsvalue (Object value) returns True if this mapping maps one or more keys to a specified value.
*----Linkedhashmap
*--hashtable
*--treemap

import Java.util.hashmap;import java.util.Map; Public classTesthashmap { Public Static voidMain (string[] args) {Map<String,String> map =NewHashmap<string,string>(); //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 elements//Take://map.remove ("Eason");//removing elements by keySystem. out. println ("whether to include Eason:"+map.containskey ("Eason")); System. out. println ("Whether it contains Jackie Chan:"+map.containsvalue ("Jackie Chan")); System. out. println ("the container has a total of"+map.size () +"a key-value pair element"); String name= map.Get("Jack");//gets the value of an element based on keySystem. out. println (name); String name2= map.Get("Jay"); System. out. println (name2); }}

There are two ways to HashMap values:

import java.util.hashmap;import java.util.map;import java.util.map.entry;import java.util.Set;/** *MAP Traversal * set<k> KeySet () returns a Set view of the keys contained in this map.  * set<map.entry<k,v>> EntrySet () returns the Set view of the mappings contained by this map. */ Public classTESTHASHMAP2 { Public Static voidMain (string[] args) {Map<String,String> map =NewHashmap<string,string>(); //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 keySet<string> KeySet =Map.keyset ();  for(String key:keyset) {String value= map.Get(key); System. out. println (key+"----"+value); } System. out. println ("-------------------------------"); //Method 2: Gets a collection of key-value pairs, and then gets the key and value from the key-value pair. (recommended)//entry<string,string>: Generic,set<entry<string,string>> of keys and values for Entry (key-value pairs) in set setsSet<entry<string,string>> EntrySet =Map.entryset ();  for(Entry<string, string>Entry:entryset) {String key= Entry.getkey ();//gets the key for the key-value pairString value = Entry.getvalue ();//get the value of a key-value pairSystem. out. println (key+"****"+value); }    }}

Java: Container/Collection (Map (HASHMAP,TREEMAP))