字符数组java的arraylist

Question

I originally have an arraylist of strings but I want to save it as an arraylist of those strings.toCharArray() instead. Is it possible to make an arraylist that stores char arrays? Here is how I tried to implement it.

String[] words = new String[]{"peter","month","tweet", "pete", "twee", "pet", "et"};
    HashMap<Integer,ArrayList<Character[]>> ordered = new HashMap<>();

    int length = 0;
    int max = 0; //max Length of words left

    for(String word: words){

        if(ordered.containsKey(length) == false){ //if int length key doesnt exist yet
             ordered.put(length, new ArrayList<Character[]>()); //put key in hashmap with value of arraylist with the one value
             ordered.get(length).add(word.toCharArray());
        }
    }

Answer 1

Note that toCharArray() returns an array of primitives ( char[] ), and not an array of the boxing class ( Character[] as you currently have). Additionally, you're only adding the given array to the map if the length of the array isn't in the map, which probably isn't the behavior you wanted (ie, you should move the line ordered.get(length).add(word.toCharArray()); outside the if statement).

Also, note that Java 8's streams can do a lot of the heavy lifting for you:

String[] words = new String[]{"peter","month","tweet", "pete", "twee", "pet", "et"};
Map<Integer, List<char[]>> ordered =
    Arrays.stream(word)
          .map(String::toCharArray)
          .collect(Collectors.groupingBy(x -> x.length));

EDIT:
As per the question in the comment, this is also entirely possible in Java 7 without streams:

String[] words = new String[]{"peter","month","tweet", "pete", "twee", "pet", "et"};
Map<Integer, List<char[]>> ordered = new HashMap<>();

for (String word: words) {
    int length = words.length();

    // if int length key doesnt exist in the map already
    List<char[]> list = orderd.get(length);
    if (list == null) {
        list = new ArrayList<>();
        orderd.put(length, list);
    }
    list.add(word);
}