Java collection------MAP (HashMap implementation)

package java_util_map;import java.util.collection;import java.util.hashmap;import  java.util.map;import java.util.map.entry;import java.util.set;public class maptest01  {Public static void main (String[] args)  {/* * map is an interface, HashMap is an implementation class of map  */Map<String, String> map = new HashMap<String, String> ();/* The  * put () method adds key-value to the map  */map.put ("0",  "Spring"), Map.put ("1",  "Summer"), Map.put (" 2 ", " Autumn ") Map.put (" 3 ", " Winter "), put in/* * hashmap, if the added key value is repeated, the method returns the old value value  */ System.out.println (Map.put ("4",  "Seasons"));/* *  print the Map object directly, you can view the ToString () method HashMap SYSTEM.OUT.PRINTLN (map);/* * containskey () returns whether it contains the specified key value  */system.out.println (Map.containskey ("2" ));//return truesystem.out.println (Map.containskey ("one"));//return false/* * containsvalue () returns whether the specified value value is included  */systEm.out.println (Map.containsvalue ("Autumn"));//return truesystem.out.println (Map.containsvalue ("222"));// Return false/* * keyset () returns a set set of all key components  */for  (string key :  Map.keyset ())  {system.out.println (key+ "--" +map.get (key) + " ");} /* * isempty () Determines whether the map is empty  */system.out.println ("is the map collection empty?").    "+map.isempty ()");/* * getordefault (Key,defaultvalue) Returns the value of the specified key, if there is no key value, Returns DEFAULVALUE&NBSP;*/SYSTEM.OUT.PRINTLN (Map.getordefault ("1",  "2"));//return summer  System.out.println (Map.getordefault ("One",  "2"));//return 2/* * size (): Returns the number of key-value pairs  */system.out.println (Map.size ());//return 5/* * values (): Returns the collection collection of value in the map  *  @return  : Spring Summer Autumn Winter Seasons */Collection< String>  values = map.values ();for  (string value : values)  { System.out.print (value +  "  ");} /* * replace (K key, v value): Replaces the value values with the old Value */system.out.println () of the specified key; Map.replace ("2",  "2");for  (String key : map.keyset ())  {system.out.println (key+ "  --> "+ map.get (key));} /* * replace (K key, v oldvalue, v newvalue): Replaces the NewValue value with the old oldValue of the specified key  *  @return: replaces the entry for the specified key only if  currently mapped to the specified value. */system.out.println ("^^ ^^ ^^ ^^ ^^ ^ ^^ ^^ ^^ ^^ ^^ ^^ ^^ ^^ "), Map.replace (" 2 ", " 2 ", " Autumn "),//return truemap.replace (" 2 ", " 1 ",   "Autumn");//return false,because the oldvalue is not correctfor (String  key : map.keyset ()) {System.out.println (key+ "-and" +map.get (key));} /* * remove (Object key): Removes the key-value */system.out.println of the specified key ("^^ ^^ ^^ ^^ ^^ ^^ ^^^^ ^^ ^^ ^^ ^^ ^^ ^ "), Map.Remove (" 0 ");for  (String key : map.keyset ())  {system.out.println ( key+ "--" +map.get (key)); /* * putifabsent (k key, v value): If the specified key is not   * already associated with a value  (or is mapped to  null)  associates it with the given value and returns null,  * else returns the current value. */system.out.println ("^^ ^^ ^^ ^^ ^^ ^^, ^^ ^^ ^^ ^^ ^^ ^^ ^^ ^ "), Map.put (" 5 ",  null), Map.putifabsent (" 5 ", " Spring ");for  (string key :  Map.keyset ())  {system.out.println (key+ "-and" +map.get (key));} /* * entryset (): Returns the set set of Key-value in the map, and the set collection is unordered and non-repeatable key-value * returns a  set view of the mappings contained in this map. */ System.out.println (^^ ^^ ^^ ^^ ^^ ^^ ^^ ^^ ^^ ^^ ^^ ^^ ^^ ^"); Set<map.entry<string, string>> mapset = map.entryset ();for  (Entry< String, string> entry : mapset)  {system.out.println (entry);}}

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Java collection------MAP (HashMap implementation)