Map is a function to save data through key-values.Correspondingly,the 'key' and the 'value' are the key words.
We usually create a Map object with HashMap,and there will be corresponding ways to save data
Map<String,Person> map = new HashMap<>();
map.put("jack", new Person("jack", 90, 15));
map.put("merry", new Person("merry", 90, 18));
And then,there also exists many methods to modify these stored data.

Map

Interface Map（映射）
HashMap

class Person implements Comparable<Person> {
    protected float score;
    protected String name;
    protected int age;

    public Person(String name,float score,int age){
        this.name = name;
        this.score = score;
        this.age = age;

    }
    @Override
    public String toString() {
        return "name:"+name+ " "+"score:" + score + " "+"age:"+age;
    }

public class MyClass {
    public static void main(String[] args) {
         /**
         *  Map - Interface Map(映射)
         *            -|HashMap     Manage the key-value pairs
         *            -|ConcurrentMap     About the safety of threads
         *            -|LinkedHashMap
         *  Dictionary key - key-value(键值对0
         *  key: 键
         *  value: 值
         *
         *  [ key: value, key: value];
         */

        // Map<String, Person> map = new HashMap<>();
        Map<String,Person> map = new HashMap<>();
        // Add a key-value
        map.put("jack", new Person("jack", 90, 15));
        map.put("merry", new Person("merry", 90, 18));

        // Get the count of key-value
        System.out.println(map.size());

        // Whether containing a 'ker'
        System.out.println(map.containsKey(("jack22")));

        //Whether containing certain 'value'
        System.out.println(map.containsValue((person)));

        // Get corresponding value of certain key
        Person p = map.get("jack");
        System.out.println("jack"+ p);

        // Delete certain key-value
        //map.remove("jack");
        System.out.println(map);

        // Take place one certain key-value
        map.replace("jack",new Person("张三",99,19));
        System.out.println(map);

        //map.clear();

        //the Traverse of map
        Set<Map.Entry<String, Person>> entries = map.entrySet();
        for(Map.Entry<String,Person> entry : entries){
        System.out.println("key:"+ entry.getKey() + " value:"+ entry.getValue());
2
false
false
jackname:jack score:90.0 age:15
{jack=name:jack score:90.0 age:15, merry=name:merry score:90.0 age:18}
{jack=name:张三 score:99.0 age:19, merry=name:merry score:90.0 age:18}
key:jack value:name:张三 score:99.0 age:19
key:merry value:name:merry score:90.0 age:18

  }
}

Here is the example

map是以键值百对来存储数据的，例如：
Map map = new HashMap();
map.put("移动","10086");
String c = map.get("移动");
结果c="10086”;
简单来说，map就像我们手机的电话本，用map.put("移动","10086")，就是在电话本保存度了移动的电话，然后当你想拿移专动的电话时候就用String c = map.get("移动")；就可以拿到电话号码了。