目录

map集合的特点

map收集遍历

方式一

方式二

HashMap与HashTable之间的区别

Map使用三层嵌套

效果图

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map集合的特点

//map集合的特点。无序，键值正确，键不能重复，值可以重复

map收集遍历

方式一

//map集合的遍历 1，获取map集合所有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);    ////通过键获得相应的值    Object value = map.get(key);    System.out.println(key "=" value);   }

方式二

//map遍历方式 2.首先取出所有保存的键值(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，不安全

hashmap 键可以为null,值也可以为null

Map使用三层嵌套

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.ot.println(key2);
				List<Student> ls = value.get(key2);
				for (Student stu : ls) {
					System.out.println(stu.getName()+"  "+stu.getFs());
				}
			}
		}

	}
}

效果图