The Map collection in Java

import java.util.collection;import java.util.hashmap;import java.util.iterator;import  java.util.map;import java.util.set;public class maptest {/** common methods for Map collection  * void  clear ();  empties Mapboolean isempty (), determines whether the collection is empty int size ();  Gets the number of key-value pairs in the map.  object put (Object key, object value);  adds a key-value pair Object get (Object key) to the collection , get Value  boolean containskey (Object key) through key;  determine if the map contains such key boolean  Containsvalue (object value);  determine if the map contains such value   object remove (Object key) ;  deletes key-value pairs by key.   collection values ();  gets all the Value  set keyset () in the map collection;   Get all the Key  set entryset () in the map; returns the  Set  view of the mappings contained in this map.      Note: The elements stored in the key section of the map collection need to be rewritten simultaneously with the Hashcode+equals method . *  @param  args */public  static void main (String[] args)  {//&nbsP TODO AUTO-GENERATED METHOD STUB//1. Creating a Map collection map personmap = new hashmap ();// 2. Add element Personmap.put ("10000",  "Nihao") to the Map collection;p ersonmap.put ("10002",  "Wobuhao");p ersonmap.put ("1000", "Wohenhao");p ersonmap.put ("10000", "Shabi"),//3. Determine the number of key-value pairs, the key in the map is unordered and non-repeatable, if repeated, overwrites the original value value System.out.println ( Personmap.size ());//4. Interprets whether a key value System.out.println (Personmap.containskey ("10000")) is included in the collection, and//5. Determines whether a value is contained in the collection. Note that the duplicate in the map, value is overridden. System.out.println (Personmap.containsvalue ("Shabi"))//6. Get valuestring key1= "10000" via key; System.out.println (Personmap.get (key1))//7. Delete the key value pair System.out.println (Personmap.size ()) by Key;p Ersonmap.remove ( Key1); System.out.println (Personmap.size ());//8. Get all value values Collection c = personmap.values (); Iterator  it = c.iterator (); while (It.hasnext ()) {System.out.println (It.next ());} 9. Get all the keys and traverse the Map Collection set key = personmap.keyset (); It = key.iterator (); object id  = null;object&Nbsp;name = null;while (It.hasnext ()) {id = it.next (); Name = personmap.get (ID); System.out.println (id+ "----->" +name);} 10. Replace the map with Set set Set maptoset = personmap.entryset (); It = maptoset.iterator (); while ( It.hasnext ()) {System.out.println (It.next ());} 11.properties//hashmap default initialization capacity is 16, the default load factor 0.75//hashtable default initialization capacity is 11, the default loading factor is 0.75//java.util.properties; It is also composed of key and value, but both key and value are string Types Properties p = new properties ();p. SetProperty ("username",   "Zhangdan");p. SetProperty ("id",  "");p. SetProperty ("Grade",  "137");//3. Fetch, get valuestring via key  v1 = p.getproperty ("Driver"); String v2 = p.getproperty ("username"); String v3 = p.getproperty ("password"); String v4 = p.getproperty ("url"); System.out.println (v1); System.out.println (v2); System.out.println (v3); SYSTEM.OUT.PRINTLN (v4);}}

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The Map collection in Java