1.键值对存储一组对象
2.key值不能重复,value可以重复
3.具体的实现类,HashMap,treeMap,HashTable,LinkedHashMap
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HashMap
数组+链表
默认的负载因子为0.75
默认数组容量大小为16
链表的默认长度为8,如果大于8会变成一个二叉树
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HashTable
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LinkedHashMap
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import java.util.HashMap; import java.util.Map; public class file { public static void main(String[] args) { stringReader(); } private static void stringReader() { Map<String,String> map = new HashMap<>(); map.put("1","lili"); map.put("2","lili2"); map.put("3","lili3"); //只会添加不存在相同key的值 map.putIfAbsent("3","lili4"); map.forEach((key,value)-> System.out.println(key+"->"+value)); } }