hashmap to arraylist

Programming Questions

clankill3r

in Programming Questions • 2 years ago

I thought there was a way to convert a hashmap to an arrayList. I have googled a lot, but i can't find the method that was like 1 syntax. Am i wrong with something? (maybe i remember something simulair from a treemap or something).

Replies(3)

fiveagon

Re: hashmap to arraylist

2 years ago

Not tested, just looking at Map

// 'V' is the Value type of the Map
Map<K, V> yourMap;
Collection<V> values = yourMap.values();
List<V> valueList = new ArrayList<V>(values);

Not sure what the 1 line solution is though. Maybe all of that put into one line?

List<V> valueList = new ArrayList<V>(yourMap.values());

fiveagon

Re: Re: hashmap to arraylist

2 years ago

For completeness' sake:

The Map interface provides three collection views, which allow a map's contents to be viewed as a set of keys, collection of values, or set of key-value mappings. The order of a map is defined as the order in which the iterators on the map's collection views return their elements. Some map implementations, like the TreeMap class, make specific guarantees as to their order; others, like the HashMap class, do not.

Set<Map.Entry<K, V>> mapEntrySet = yourMap.entrySet();
Set<K> keySet = yourMap.keySet();
Collection<V> valueCollection = yourMap.values();

Every one of these can be used as the argument to an ArrayList constructor (or any Collection implementation's constructor!), as long as the Generic types match.

clankill3r

Re: hashmap to arraylist

2 years ago

your correct!

ArrayList<Word> words = new ArrayList<Word>(hm_words.values());

thanks

Top Reply