Can't add chars to Character ArrayList

Question

I'm having issues understanding ArrayList in Java. I tried to declare a Character ArrayList and add a char at 0, but it returned error at list.add(0, "B") line.

public class ArrListTest {
public static void main(String[] args) {
    ArrayList<Character> list;
    list.add(0, "B");
 }
}

Also I'm having issues reversing a string. Is there a way to reverse a string without using a loop?

If you would use google to search for 'Java reverse string', you would find at least one concise one-liner. — 11684, Jul 20 '14 at 13:40

score 3 · Accepted Answer · edited May 23 '17 at 12:27

"B" is instance of String, characters need to be surrounded with ' like 'B'.

use

list.add(0,'B');

If you want to add B after last element of list skip 0

list.add('B');

Also don't forget to actually initialize your list

List<Character> list = new ArrayList<>();
//                   ^^^^^^^^^^^^^^^^^^^

To know why I used List<Character> list as reference type instead of ArrayList<Character> list read:
What does it mean to “program to an interface”?

Reimeus · Answer 2 · 2014-07-20T13:42:26.997

3

You're mixing up List.set with List.add. Use a character literal instead of a String and use

list.add('B');

after initializing the List

List<Character> list = new ArrayList<>();

edited Jul 20 '14 at 13:42

answered Jul 20 '14 at 13:36

Reimeus

158,255
15
216
276

score 0 · Answer 3 · answered Jul 23 '19 at 09:27

public class stackQuestions {

public static void main(String args[]) {

    ArrayList list = new ArrayList();

    list.add("b");
    list.add(0, "a");// it will add to index 0
    list.add(0, "c");// it will replaces to index 0
    System.out.println(list);
}

}

score -1 · Answer 4 · answered Jul 22 '19 at 06:17

-1

public static void main(String args[]) {

    ArrayList list= new ArrayList();
        list.add("B");

}

try this

answered Jul 22 '19 at 06:17

KARTHIK SARAGADAM

1
1

This only works for the first character you insert. The second one will not be placed at index 0. – BDL Jul 22 '19 at 08:15
list.add("b"); list.set(0, "a"); by this we can replace – KARTHIK SARAGADAM Jul 23 '19 at 09:24
op has to insert **a number of characters at index 0*. You approach (add) does only work for the first character you add to the list. Afterwards they are appended to the end and not at the beginning. – BDL Jul 23 '19 at 09:25

Can't add chars to Character ArrayList

4 Answers4