python和java对字典空键处理的区别

1.Java HashMap　　

 

即使没有null这个键值，map.get(null)是允许的, 默认返回null.

null可作为HashMap键值。

 

import java.util.HashMap;

public class StudyJava {

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        HashMap<Integer,String> map = new HashMap<>();
        map.put(1,"hello world");
        System.out.println(map);
        System.out.println(map.get(null));
        map.put(null,"1");
        System.out.println(map.get(null));
    }

}

{1=hello world}
null
1

 

2.python dict

 

允许None作为键

没有默认的None键对应的值，会raise KeyError

a = {}
a[1] = 2
a
a[None] 

　{1: 2}

KeyError Traceback (most recent call last)
<ipython-input-56-308db02c468a> in <module>
----> 1 a[None]

KeyError: None

a[None] = 3
a

{1: 2, None: 3}