Map集合及三层嵌套

一.Map集合介绍

1.定义:无序,以键值(key,value)对的形式存储数据,键唯一,值不唯一;
注意:
  1)键key的底层结构为Set集合,其特征之一是无序;
  2)值value的底层结构为Collection集合,其特征之一是对象可重复;
  3)Map集合不继承Collection接口

2.遍历方式(3种):
  1)获取键key
  2)获取值value
  3)获取键值对

//定义一个Map集合,key和value不规定类型，任意放入数据，用keySet()和entrySet()及value()3种方式遍历出Map集合的数据

		Map<String, Student> map=new HashMap<>();
		
		map.put("T22", new Student("梅子1", 88.8));
		map.put("T23", new Student("梅子2", 88.8));
		map.put("T24", new Student("梅子3", 88.8));
		map.put("T25", new Student("梅子4", 88.8));
		map.put("T26", new Student("梅子5", 88.8));
		
		//获取键
		Set<String> ks = map.keySet();
		
		System.out.println("--------键遍历-------------------");
		
		for (String str : ks) {
			Student stu = map.get(str);
			System.out.println(str+","+stu.getSname()+","+stu.getScore());
		}
		
		System.out.println("----------值遍历------------");
		
		Set<Entry<String, Student>> es = map.entrySet();
		/*for (Entry sr : es) {
			System.out.println(sr);
		}*/
		Iterator<Entry<String, Student>> it2 = es.iterator();
		
		while(it2.hasNext()) {
			System.out.println(it2.next());
		}
//		定义一个Map集合,key和value不规定类型，任意放入数据,单独拿到所有的value的数据
		
		System.out.println("----------单独取值-----------------");
		
		Map<String, String> map2=new HashMap<>();
		
		map2.put("a", "君君1");
		map2.put("b", "君君2");
		map2.put("c", "君君3");
		map2.put("d", "君君4");
		
		Set<Entry<String, String>> es2 = map2.entrySet();
	
		/*for (Entry st : es2) {
			System.out.println(st);
		}*/
		System.out.println("----------键值对-----------------");
		Iterator<Entry<String, String>> it = es2.iterator();
		
		while(it.hasNext()) {
			System.out.println(it.next());
		}

二.案例:Map集合三层嵌套

public static void main(String[] args) {

		Map<String, Map<String, List<Student>>> map = new HashMap<>();

		// 每一个部

		Map<String, List<Student>> m1 = new HashMap<>();// 初中部
		Map<String, List<Student>> m2 = new HashMap<>();// 高中部
		Map<String, List<Student>> m3 = new HashMap<>();// 大学部

		// 初中部

		List<Student> lst1 = new ArrayList<>();
		lst1.add(new Student("张晓东", 90.3));
		lst1.add(new Student("张晓西", 70.3));

		List<Student> lst2 = new ArrayList<>();
		lst2.add(new Student("张晓北", 90.3));
		lst2.add(new Student("张晓南", 82.3));

		m1.put("T110", lst1);
		m1.put("T111", lst2);

		map.put("初中部", m1);

		// 高中部

		List<Student> lst3 = new ArrayList<>();
		lst3.add(new Student("张三", 90.3));
		lst3.add(new Student("李四", 70.3));

		List<Student> lst4 = new ArrayList<>();
		lst4.add(new Student("王五", 90.3));
		lst4.add(new Student("小六", 82.3));

		List<Student> lst5 = new ArrayList<>();
		lst5.add(new Student("小八 ", 90.3));
		lst5.add(new Student("小酒", 82.3));

		m2.put("T206", lst3);
		m2.put("T222", lst4);
		m2.put("T208", lst5);

		map.put("高中部", m2);

		// 大学部

		List<Student> lst6 = new ArrayList<>();
		lst6.add(new Student("可乐", 90.3));
		lst6.add(new Student("雪碧", 70.3));

		List<Student> lst7 = new ArrayList<>();
		lst7.add(new Student("哇哈哈", 90.3));
		lst7.add(new Student("老干妈", 82.3));

		m3.put("T230", lst6);
		m3.put("T231", lst7);

		map.put("大学部", m3);

		Set<String> ks = map.keySet();

		for (String str : ks) {

			Map<String, List<Student>> mp = map.get(str);

			Set<Entry<String, List<Student>>> sy = mp.entrySet();

			for (Entry<String, List<Student>> sr : sy) {
				String key = sr.getKey();
				List<Student> val = sr.getValue();
				Iterator<Student> it5 = val.iterator();
				while (it5.hasNext()) {
					System.out.println(it5.next() + "," + key + "," + str);
				}
			}

		}

	}

三.TreeMap排序

Map<String, String> map2=new HashMap<>();
		
		map2.put("a", "君君1");
		map2.put("b", "君君2");
		map2.put("c", "君君3");
		map2.put("d", "君君4");
		
		Set<Entry<String, String>> es2 = map2.entrySet();
	
		/*for (Entry st : es2) {
			System.out.println(st);
		}*/
		System.out.println("----------键值对-----------------");
		Iterator<Entry<String, String>> it = es2.iterator();
		
		while(it.hasNext()) {
			System.out.println(it.next());
		}
		
//		定义一个Map集合,key和value不规定类型，针对集合中的元素进行排序
		
		System.out.println("------------键排序------------------------");
		
		TreeMap<String, Student> tmap=new TreeMap<>();
		
		tmap.put("d", new Student("梅子4", 88.84));
		tmap.put("c", new Student("梅子3", 88.83));
		tmap.put("b", new Student("梅子1", 88.81));
		tmap.put("a", new Student("梅子2", 88.82));
		
		Set<String> ksd = tmap.keySet();
		
		Iterator<String> it3 = ksd.iterator();
		
		while(it3.hasNext()) {
			System.out.println(it3.next());
		}
		
		System.out.println("------------值排序-------------------------");
		
		/*Collection va = tmap.values();
		
		Iterator it4 = va.iterator();
		
		while(it4.hasNext()) {
			System.out.println(it4.next());//其实也是根据键排序
		}*/
		
		System.out.println("------------键值对排序-------------------------");
		
		Set<Entry<String, Student>> es3 = tmap.entrySet();
		
		Iterator<Entry<String, Student>> it4 = es3.iterator();
		
		while(it4.hasNext()) {
			System.out.println(it4.next());//也是根据键排序
		}