Java collections convert a string to a list of characters

Question

I would like to convert the string containing abc to a list of characters and a hashset of characters. How can I do that in Java ?

List<Character> charList = new ArrayList<Character>("abc".toCharArray()); 

Answer 1

In Java8 you can use streams I suppose. List of Character objects:

List<Character> chars = str.chars()     .mapToObj(e->(char)e).collect(Collectors.toList()); 

And set could be obtained in a similar way:

Set<Character> charsSet = str.chars()     .mapToObj(e->(char)e).collect(Collectors.toSet()); 

Answer 2

You will have to either use a loop, or create a collection wrapper like Arrays.asList which works on primitive char arrays (or directly on strings).

List<Character> list = new ArrayList<Character>(); Set<Character> unique = new HashSet<Character>(); for(char c : "abc".toCharArray()) {     list.add(c);     unique.add(c); } 

Here is an Arrays.asList like wrapper for strings:

public List<Character> asList(final String string) {     return new AbstractList<Character>() {        public int size() { return string.length(); }        public Character get(int index) { return string.charAt(index); }     }; } 

This one is an immutable list, though. If you want a mutable list, use this with a char[]:

public List<Character> asList(final char[] string) {     return new AbstractList<Character>() {        public int size() { return string.length; }        public Character get(int index) { return string[index]; }        public Character set(int index, Character newVal) {           char old = string[index];           string[index] = newVal;           return old;        }     }; } 

Analogous to this you can implement this for the other primitive types. Note that using this normally is not recommended, since for every access you would do a boxing and unboxing operation.

The Guava library contains similar List wrapper methods for several primitive array classes, like Chars.asList, and a wrapper for String in Lists.charactersOf(String).