集合：Collection
Map：键值对key-value映射表（默认
HashMap
Hashtable
concurrentHashMap
LinkedHashMap
SortedMap（I)->TreeMap
1.HashMap
Map<String,String>map=newHashMap<String,String>();
//增删改查
map.put(“hehe”,“123”);//增加，返回被替换的value值
map.put(“hehe”,“1234”);