二、Map

import java.util.ArrayList;
import java.util.Arrays;
import java.util.HashMap;
import java.util.Map;
// import java.util.*;
import java.util.Set;

public class Hello {

public static void main(String[] args) {
    Map<String, String> map = new HashMap<String, String>();
    // Map<String, String> map = new HashMap();
    map.put("1", "hello");
    map.put("2", "world");
    map.put("3", "vinter");
    System.out.println(map);

    String mv = map.remove("1");
    System.out.println(map);
    System.out.println(mv);

    String hi = map.put("2", "hi");
    System.out.println(map);
    System.out.println(hi);


    String en = map.get("3");
    System.out.println(en);  
    System.out.println("-------------");
    
    Set<String> list = map.keySet();

    for(String key : list) {
        System.out.println(map.get(key)); 
    }

}

}