18th Day of Java Learning (map collection)

A map collection is an object that maps keys to values. A map cannot contain duplicate keys, and each key can be mapped to at most one value. A key-value pair is stored in the form of an element, the key is unique, the value can be repeated, a bit similar to the primary key in the database plus data. The main functions are:

A: Add Features

Put method
B: Delete Feature

Remove method

C: Judging function

Boolean ContainsKey (Object key)//Determine if a key is included

Boolean containsvalue (Object Value)

Boolean IsEmpty ()
D: Get Features

Get method//Example Description

E: Length function

Map<string,string> HM = new hashmap<string,string> ();

Hm.put ("it002", "Hello");
Hm.put ("it003", "World");
Hm.put ("it001", "Java");

Mode 1 Key Find value
set<string> set = Hm.keyset ();
for (String Key:set) {
String value = Hm.get (key);
System.out.println (key+ "---" +value);
}

Method 2 Key value to object find key and value
Set<map.entry<string,string>> Set2 = Hm.entryset ();
for (map.entry<string,string> Me:set2) {
String key = Me.getkey ();
String value = Me.getvalue ();
System.out.println (key+ "---" +value);

18th Day of Java Learning (map collection)