Basically, it allows you to do this:

callAPIThatTakesAMap(Collections.singletonMap(key, value));

rather than this:

Map
    
      m = new HashMap
     
      ();m.put(key, value);callAPIThatTakesAMap(m);
     
    

which is much nicer when you only have a single key/value pair. This situation probably does not arise very often, but singleton() and singletonList() can quite frequently be useful.

参考 :