如何将单词存储为 TreeMap 中的键？

Question

Using a TreeMap, how would I use a comparator to map keys which are words to corresponding linked lists.

TreeMap<String, LinkedList<String>()> () words = new TreeMap(<Comparator> );

Is there a specific comparator I can use or do I have to implement a way for it to alphabetically sort the words I add to the TreeMap?

Answer 1

No need for a Comparator .

As a NavigableMap , a TreeMap promises to keep its keys sorted.

And String class, the class of your map's keys, already implements Comparable . So string objects know how to be sorted. With keys that are Comparable , you need not specify a Comparator .

Also, generally best to declare your collection in a more general way using interfaces or superclasses. This leaves room for you to change your concrete classes later without breaking other code. So NavigableMap< String, List< String > > map rather than TreeMap< String, LinkedList< String > > map .

For example, in code below we are free to use List.of to produce a List of some unknown concrete class rather than being limited to only LinkedList as seen in your code.

NavigableMap< String , List< String > > map = new TreeMap<>() ;

Example usage.

map.put( "animals" , List.of( "dog" , "cat" , "bird" ) ) ;
map.put( "people" , List.of( "Alice" , "Bob" , "Carol" ) ) ;
map.put( "cars" , List.of( "Honda" , "Mazda" ) ) ;

See this code run live at IdeOne.com .

map.toString() ➡ {animals=[dog, cat, bird], cars=[Honda, Mazda], people=[Alice, Bob, Carol]}

Note how the "cars" entry has been sorted from 3rd-added to the 2nd position, between "animals" and "people" alphabetically.