Three super-hard-to-remember conveniences for HASHMAP collections in Java

HashMap and HashSet are two important members of the Java Collection Framework, where HashMap is the common implementation class of the Map interface

1: Create a class first

 1  package   day;  2   Import  java.util.ArrayList; import  Java.util.HashMap; import  java.util.Iterator; import  Java.util.Map; import  java.util.Map.Entry; import   Java.util.Set;  4   Import   Javax.swing.JComboBox.KeySelectionManager;  6   Public  class  Text {

When created, the second step begins.

2: Use HashMap to store information from multiple countries of course it has to be written in the Main method

 Public Static void Main (string[] args) {    1     map<string,string>map=new hashmap<string,string> ();

3: Add the country we want to add in HashMap
To establish a key-value mapping between a national abbreviation and a Chinese name, such as CN counterpart → China, can be found in China according to "cn", delete can be deleted, let us do the next step

1 map.put ("CN", "China"); 2         Map.put ("USA", "USA"); 3         Map.put ("UD", "United Nations");

Add the element with the put method above, consistent with the Add method of the other collection (linkedlist,arraylist), but there is no Add method in the method of map here.

4: The first solution to add, this method is also difficult

System.out.print (Map.size ());          for (entry<string, string> item:map.entrySet ()) {            System.out.println (String.Format ("key is%s\ Nvalues is%s ", Item.getkey (), Item.getvalue ()));                    }

The second scenario:

set<string>keyset=Map.keyset ();          for (String key:keyset) {                        System.out.println ("key is" +key+ "\nvalue is" +Map.get (key));        }

The third scenario:

set<string>set=Map.keyset ();               Iterator<string>iterator=set.iterator ();                 while (Iterator.hasnext ()) {        String key=iterator.next ();        System.err.println ("key is" +key+ "value is" +Map.get (key));                  }

Three super-hard-to-remember conveniences for HashMap collections in Java