map集合

最新推荐文章于 2023-07-18 11:57:53 发布

T275fuyou

最新推荐文章于 2023-07-18 11:57:53 发布

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文章标签：蓝桥杯 eureka postman

本文链接：https://blog.youkuaiyun.com/T275fuyou/article/details/124874232

HashMap与HashTable之间的区别

Map集合3层嵌套使用

效果图

map集合的特点

//map集合的特点。无序，键值对,键不可以重复，值可以重复

map集合遍历方式

方式一

//map集合的遍历方式 1，获取map集合中的所有key的set集合，再通过key获取值
        Set<String> keySet = map.keySet();
        
        for (String key : keySet) {
            //System.out.println(key);
            //通过键获取对应的值
            Object value = map.get(key);
            System.out.println(key+"="+value);
        }

方式二

//map遍历方式 2.先取出所有保存所有键值对(Entry)的set，在遍历此set即可
		
		Set<Entry<String, Object>> entrySet = map.entrySet();
		
		for (Entry<String, Object> entry : entrySet) {
			System.out.println(entry);
			System.out.println(entry.getKey());
			System.out.println(entry.getValue());
		}

HashMap与HashTable之间的区别

同步既排队线程安全的

hashtable 键不可以为null,值也不能null

异步，非安全的

hashmap 键可以为null,值也可以为null

Map集合3层嵌套使用

package com.zking.aa;

import java.util.HashMap;
import java.util.LinkedList;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Set;

public class zy4 {
	
	public static void main(String[] args) {
		
		List<Student> ls1 = new LinkedList<Student>();
		List<Student> ls2 = new LinkedList<Student>();
		List<Student> ls3 = new LinkedList<Student>();
		List<Student> ls4 = new LinkedList<Student>();
		List<Student> ls5 = new LinkedList<Student>();
		List<Student> ls6 = new LinkedList<Student>();
		List<Student> ls7 = new LinkedList<Student>();
		ls1.add(new Student("张晓东",90));
		ls1.add(new Student("张晓西",75));
		ls2.add(new Student("张晓北",80));
		ls2.add(new Student("张晓南",82));
		ls3.add(new Student("张三",90));
		ls3.add(new Student("李四",100));
		ls4.add(new Student("王五",70));
		ls4.add(new Student("小六",100));
		ls5.add(new Student("小八",70));
		ls5.add(new Student("小九",100));
		ls6.add(new Student("可乐",60));
		ls6.add(new Student("雪碧",50));
		ls7.add(new Student("哇哈哈",90));
		ls7.add(new Student("老干妈",80));
		
		Map<String, List<Student>> amap = 
				new HashMap<String,List<Student>>();
		amap.put("T110", ls1);
		amap.put("T111", ls2);
		Map<String, List<Student>> bmap = 
				new HashMap<String,List<Student>>();
		bmap.put("T206", ls3);
		bmap.put("T222", ls4);
		bmap.put("T208", ls5);
		Map<String, List<Student>> cmap = 
				new HashMap<String,List<Student>>();
		cmap.put("T230", ls6);
		cmap.put("T231", ls7);
		

		Map<String, Map<String,List<Student>>> map = 
				new HashMap<String, Map<String,List<Student>>>();
		map.put("卓京小学部", amap);
		map.put("卓京初中部", amap);
		map.put("卓京大学部", amap);
		
		Set<String> keySet = map.keySet();
		for (String key : keySet) {
			Map<String, List<Student>> value = map.get(key);
			System.out.println(key);
			Set<String> keySet2 = value.keySet();
			for (String key2 : keySet2) {
				System.out.println(key2);
				List<Student> ls = value.get(key2);
				for (Student stu : ls) {
					System.out.println(stu.getName()+"  "+stu.getFs());
				}
			}
		}

	}
}