An empty string can be used as the key of hashmap.

In Java, an empty string can be used as the key of hashmap with the string type as the key, for example:

Public static void main (string [] ARGs) {// todo auto-generated method stubsystem. out. println ("----->"); hashmap <string, string> mfilecache = new hashmap <string, string> (); mfilecache. put ("", "Null String"); mfilecache. put ("ABC", "ABC string"); system. out. println ("[" + mfilecache. get ("") + "]"); system. out. println ("[" + mfilecache. get ("ABC") + "]"); system. out. println ("<-----");}

The output result is as follows:

----->
[Null String]
[ABC string]
<-----

In addition, hashmap also runs the null key and null value. The following describes hashmap in JDK:

Java. util. hashmap <K, V>

Type parameter:

K-The type of the key maintained by this ing

V-Type of the mapped Value

Hash table-basedMapInterface implementation. This implementation provides all the optional ing operations and allows the useNullValue andNullKey. (Except for non-synchronization and allow the use of null,HashmapClass andHashtable.) This class does not guarantee the order of mappings, especially it does not guarantee that the order remains unchanged.