question: public static Set < String > putSetIntoMap ( String key , Map < String , Set < String > > map , String value ) { Set < String > set = new HashSet < String > ( ) ; set . add ( value ) ; map . put ( key , set ) ; return set ; }
target:  Returns set of string. This is a convenient method for adding a set of  string into a map. In this project, we usually have the  <code>Map&lt;String, Set&lt;String&gt;&gt; and many times, we just  want to add a string to the map.