Map and its sub-classes

 Packagecom. Map;Importjava.util.Collection;ImportJava.util.HashMap;ImportJava.util.Iterator;ImportJava.util.Map;ImportJava.util.Map.Entry;ImportJava.util.Set;/* * Introduce map * We know that the collection is for storing objects. The collection collection is characterized by storing objects in which each value is an object * when encountering this situation: * For example: Students in the school, how to query it? According to the number of students * if you are using collection saved data, you need to traverse collection all students, and then find the corresponding student's content * If you are using a map collection, you can specifically put the student ID, because it is unique, as a key, Then iterate through all the keys, find the * corresponding key, and then indicate the student information corresponding to the key. * I feel that using map to store data simplifies query time.      * * map<k,v> Mapping Entries (key value pairs) * Key is not repeatable, the data structure of map is only related to key, value is stored in the key * * Map<k,v> method * * * Object put (key,value)//returns the original value in the key * Putall (MAP&LT;? extends K,? extends v> m) add all the mappings in M to this map, and if there is a key, replace the * Delete: * Clear () * Remove (object key)//delete the key value of the specified key pair * judgment: * ContainsKey (Object key) * Containsvalue ( Object key) * Equals (Object o) * hashcode () * ISEMPTY () * Get: * set<map.entry<k,v>>      EntrySet () returns the set view of the mappings contained in this map * get (Object key) Gets the property value of the corresponding key in the map * set<k> KeySet () returns the set set of keys in this map *  Collection<v> values () returns the Collection view of the values contained in this map * size () returns the number of key-value mappings in this map*/ Public classStudy01 { Public Static voidMain (string[] args) {Map<Integer,String> map=NewHashmap<integer,string>(); Map<Integer,String> map1=NewHashmap<integer,string>(); //put (k,v)System.out.println ("Put:" +map.put (1, "Guodaxia")); Map.put (1, "Guoxiaoxia"); Map1.put (1, "Aao"); Map1.put (2, "Qaq");//Qaq cry, sell Moe//PutallMap.putall (MAP1); SYSTEM.OUT.PRINTLN (map);//overridden the ToString//Remove (Object key)//System.out.println ("Remove:" +map.remove (1));//System.out.println (map); //Clear ()//map.clear ();//System.out.println (map);System.out.println (Map.containskey (1)); System.out.println (Map.containsvalue ("Qaq")); //get (Key)System.out.println (Map.get (1));; //KeySet ()Set<integer> keys=Map.keyset ();  for(intI:keys) {System.out.println (i+"---"+Map.get (i)); }        //values ()Collection<string> l=map.values ();  for(Iterator<string> it=l.iterator (); It.hasnext ();) {System.out.println (It.next ()); }                //set<map.entry<k,v>> EntrySet () returns a Set view of the mappings contained in this map//map.entry<k,v> is an interface whose implementation class stores a pair of mapped values Key--value, which you understand as an object that stores key-value pairs//several of its methods://GetKey ()//GetValue ()//toString ()//SetValue ()//hashcode ()//equals ()//It is similar to an iterator in collection and can be described as a unique iterator to the map collection, so you can also modify the contents of the collection by thisSet<entry<integer,string>> s=Map.entryset ();  for(entry<integer,string>ss:s) {System.out.println (Ss.getkey ()+ "\ T" +Ss.getvalue ()); }         for(entry<integer,string>ss:s) {            if(Ss.getkey () ==2) {Ss.setvalue ("Haha");            }} System.out.println (map); }} Packagecom. Map;/** * HASHMAP HASH Table structure * * Linkedhashmap bottom is hash table and linked list, ordered unique * * TREEMAP * key is red black tree structure has a specific order, unique * sort and unique with sort method * Natural sort is entity class implements the comparable interface * Sequencer implementation. * To create the sequencer, the sequencer is a class that implements the comparator interface * When the TREEMAP is created, the constructor is used to enter the sequencer*/ Public classStudy02 {}

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Map and its sub-classes