Converting Char Array to List in Java

Question

Can anyone help me and tell how to convert a char array to a list and vice versa. I am trying to write a program in which users enters a string (e.g "Mike is good") and in the output, each whitespace is replaced by "%20" (I.e "Mike%20is%20good"). Although this can be done in many ways but since insertion and deletion take O(1) time in linked list I thought of trying it with a linked list. I am looking for someway of converting a char array to a list, updating the list and then converting it back.

public class apples {    public static void main(String args[])    {       Scanner input = new Scanner(System.in);       StringBuffer sb = new StringBuffer(input.nextLine());        String  s = sb.toString();       char[] c = s.toCharArray();       //LinkedList<char> l = new LinkedList<char>(Arrays.asList(c));       /* giving error "Syntax error on token " char",          Dimensions expected after this token"*/     } } 

So in this program the user is entering the string, which I am storing in a StringBuffer, which I am first converting to a string and then to a char array, but I am not able to get a list l from s.

I would be very grateful if someone can please tell the correct way to convert char array to a list and also vice versa.

Answer 1

In Java 8 and above, you can use the String's method chars():

myString.chars().mapToObj(c -> (char) c).collect(Collectors.toList()); 

And if you need to convert char[] to List<Character>, you might create a String from it first and then apply the above solution. Though it won't be very readable and pretty, it will be quite short.

Answer 2

Because char is primitive type, standard Arrays.asList(char[]) won't work. It will produce List<char[]> in place of List<Character> ... so what's left is to iterate over array, and fill new list with the data from that array:

    public static void main(String[] args) {     String s = "asdasdasda";     char[] chars = s.toCharArray();      //      List<Character> list = Arrays.asList(chars); // this does not compile,     List<char[]> asList = Arrays.asList(chars); // because this DOES compile.      List<Character> listC = new ArrayList<Character>();     for (char c : chars) {         listC.add(c);     } } 

And this is how you convert List back to array:

    Character[] array = listC.toArray(new Character[listC.size()]); 

Funny thing is why List<char[]> asList = Arrays.asList(chars); does what it does: asList can take array or vararg. In this case char [] chars is considered as single valued vararg of char[]! So you can also write something like

List<char[]> asList = Arrays.asList(chars, new char[1]); :)