map

HashMap
...
import java.util.Map;

public class HashMapDemo {
public static void main(String[] args) {
HashMap map = new HashMap<>();//<>钻石语法
map.put(1,"hahah");
map.put(2,"hehe");
map.put(3,"heihei");
map.put(4,"huihui");

    System.out.println(map);

    for (Map.Entry  e : map.entrySet()){
        System.out.println(e.getKey()+"="+e.getValue());

    }
    for (Integer i : map.keySet()){
        System.out.println(i+"="+map.get(i)+"\t");
    }
    System.out.println();
    for (String v: map.values()){
        System.out.println(v+"\t");
    }

}

}
...
TreeMap
...
package edu.xcdq.map;

import java.util.Map;
import java.util.TreeMap;

public class TreeMapDemo {
public static void main(String[] args) {
TreeMap map = new TreeMap<>();
map.put(1,"hahah");
map.put(2,"hehe");
map.put(3,"heihei");
map.put(4,"huihui");

    System.out.println(map);

    for (Map.Entrye: map.entrySet()){
        System.out.println(e.getKey()+"="+e.getValue()+"\t");
    }
    System.out.println();
    for (Integer i:map.keySet()){
        System.out.println(i+"="+map.get(i)+"\t");
    }
    System.out.println();

    for (String v: map.values()){
        System.out.println(v+"\t");

    }

    System.out.println();

    System.out.println("firstKey=>"+map.firstKey());
    System.out.println("firstEntry=>"+map.firstEntry());
    System.out.println("lastKey=>"+map.lastKey());
    System.out.println("lastEntry=>"+map.lastEntry());
}

}
...