Map 接口

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));
    }
}