集合嵌套案例分析

代码：

package com.itheima.day27_Collection_nesting;

import java.util.*;

/*目标:理解集合的嵌套。
江苏省 ="南京市","扬州市","苏州市","无锡市","常州市"
湖北省 ="武汉市","孝感市","十堰市","宜昌市","鄂州市"
河北省 ="石家庄市","唐山市","邢台市","保定市","张家口市"
*/
public class CollectionNestingTest {
    public static void main(String[] args) {
        // 1、定义一个Map集合存储全部的省份信息，和其对应的城市信息。
        Map<String, List<String>> map= new HashMap<>();

        List<String> cities1 = new ArrayList<>();
        Collections.addAll(cities1,"南京市","扬州市","苏州市","无锡市","常州市");
        map.put("江苏省",cities1);

        List<String> cities2 = new ArrayList<>();
        Collections.addAll(cities2,"武汉市","孝感市","十堰市","宜昌市","鄂州市");
        map.put("湖北省",cities2);

        List<String> cities3 = new ArrayList<>();
        Collections.addAll(cities3,"石家庄市","唐山市","邢台市","保定市","张家口市");
        map.put("河北省",cities3);

        System.out.println(map);

        List<String> citis = map.get("湖北省");
        for (String citi : citis) {
            System.out.println(citi);
        }

        map.forEach((p,c)->{
            System.out.println(p+"--------->"+c);
        });

    }
}