数据结构集，列表，地图还是树？

Question

I am trying to choose a Java data structure with the following properties

Key: Long

Value: Set

Is there a structure that I can index into and add values to the Set?

For example say I have the object <1, [a,b,c]> and I want to add d this so that the output is <1, [a,b,c,d]>?

Can this be easily done in java?

Answer 1

If you are able to use a third party library, Guava has Multimaps, which make it easy to store multiple values for a single key.

For example:

    import com.google.common.collect.HashMultimap;

    HashMultimap<Long, String> multimap = HashMultimap.create();
    multimap.put(1L, "a");
    multimap.put(1L, "b");
    multimap.put(1L, "c");
    multimap.put(1L, "d");

See the docs .

Answer 2

As others have stated, you will be best served by a Map<Long, Set<String>> . In your example:

Map<Long, Set<String>> myMap = new HashMap<Long, Set<String>>(); 
Set<String> initialSet = new HashSet<String>();
initialSet.add("a");
initialSet.add("b");
initialSet.add("c");
myMap.put(1, initialSet);
myMap.get(1).add("d"); // to add the "d"

Answer 3

I have the object <1, [a,b,c]> and I want to add d this so that the output is <1, [a,b,c,d]> ?

Map<Long, Set<Character>

would work good

Answer 4

是的，地图可以工作。

Map yourmap = new HashMap<Long, List<String>>();

Answer 5

Just use:

HashMap<Long, String> map = new HashMap<Long, ArrayList<String>>();

If you want to add something to it just

ArrayList<String> list = map.get(KEY_YOU_WANT_TO_CHECK);
if(list == null){
    list = new ArrayList<String>();
    list.add(STRING_YOU_WANT_TO_ADD);
    map.put(KEY_YOU_WANT_TO_CHECK,list);
}else{
    list.add(STRING_YOU_WANT_TO_ADD);
}

Of course you can replace ArrayList with HashSet also with Vector and TreeSet