How to convert ArrayList of Strings to char array

Question

The following code converts ArrayList<String> to char[] and print output which appears as [back, pack]. Here, the char[] includes ',' and ' '. Is there a way to do it in another way to get rid of comma and space?

ArrayList<String> list = new ArrayList<String>();
list.add("back");
list.add("pack");

char[] chars = list.toString().toCharArray();

for (char i : chars){
   System.out.print(i);
}

It's not a good idea in general to rely on the behaviour of toString. Whilst something like ArrayList is unlikely to change the implementation of toString, other classes might, which would mean any code you write relying it it will no longer work as expected. — Mark Chorley, Feb 03 '16 at 10:13

score 4 · Accepted Answer · edited Feb 03 '16 at 10:43

4

Just replace the this line

char[] chars = list.toString().toCharArray();

with below two lines

String str=list.toString().replaceAll(",", "");
char[] chars = str.substring(1, str.length()-1).replaceAll(" ", "").toCharArray();

edited Feb 03 '16 at 10:43

Robert

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answered Feb 03 '16 at 10:37

Shomil Khare

91
2

Hey just one question if I may, that why can't we replace both the space and comma as if they were one – Prabhat Gaur May 03 '23 at 15:36

hotkey · Answer 2 · 2016-02-29T11:47:32.753

You can do it by joining the Strings in your ArrayList<String> and then getting char[] from the result:

char[] chars = list.stream().collect(Collectors.joining()).toCharArray();

Here .stream.collect(Collectors.joining()) part is Java 8 Stream way to join a sequence of Strings into one. See: Collectors.joining() docs.

If you want any delimiter between the parts in the result, use Collectors.joining(delimiter) instead.

There's also an overload which adds prefix and suffix to the result, for example, if you want [ and ] in it, use Collectors.joining("", "[", "]").

mohammedkhan · Answer 3 · 2016-02-03T13:56:03.253

2

Your toString method on list is what is adding the comma and space, it's a String representation of your list. As list is a collection of Strings you don't need to call toString on it, just iterate through the collection converting each String into an array of chars using toCharArray (I assume you will probably want to add all the chars of all the Strings together).

edited Feb 03 '16 at 13:56

answered Feb 03 '16 at 10:09

mohammedkhan

953
6
14

The answer doesn't provide a way to convert `ArrayList` to `char[]`. – hotkey Feb 03 '16 at 12:56
That is true, it was sort of implied by "manipulate the data how you want it". I was trying to point out the error he was getting. I'll amend the answer though. – mohammedkhan Feb 03 '16 at 13:52

score 2 · Answer 4 · edited Feb 03 '16 at 11:14

2

String to charArray in Java Code:

ArrayList<String> list = new ArrayList<String>();
ArrayList<Character> chars = new ArrayList<Character>();
list.add( "back" );
list.add( "pack" );
for ( String string : list )
{
    for ( char c : string.toCharArray() )
    {
        chars.add( c );
    }
}
System.out.println( chars );

edited Feb 03 '16 at 11:14

Mohammad Faisal

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answered Feb 03 '16 at 11:12

Anand Pandey

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score 0 · Answer 5 · edited May 23 '17 at 12:18

Just an example how should you resolved large list to array copy. Beware number of characters must be less then Integer.MAX. This code is just an example how it could be done. There are plenty of checks that one must implement it to make that code works properly.

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

public class WrappedList {

    //Or replace with some better counter
    int totalCharCount = 0;
    final List<String> list;

    public WrappedList() {
        this(new ArrayList<String>());
    }

    public WrappedList(final List<String> list) {
        this.list = list;
    }

    public void add(final String toAdd) {
        if(toAdd != null) {
            totalCharCount += toAdd.length();
            this.list.add(toAdd);
        }
    }

    public List<String> getList() {
        return Collections.unmodifiableList(list);
    }

    public char[] toCharArray() {
        return this.toCharArray(this.totalCharCount);
    }


    public char[] toCharArray(final int charCountToCopy) {
        final char[] product = new char[charCountToCopy];
        int buffered = 0;
        for (String string : list) {
            char[] charArray = string.toCharArray();
            System.arraycopy(charArray, 0, product, buffered, charArray.length);
            buffered += charArray.length;
        }
        return product;
    }

    //Utility method could be used  also as stand-alone class
    public char[] toCharArray(final List<String> all) {
        int size = all.size();
        char[][] cpy = new char[size][];
        for (int i = 0; i < all.size(); i++) {
            cpy[i] = all.get(i).toCharArray();
        }
        int total = 0;
        for (char[] cs : cpy) {
            total += cs.length;
        }
        return this.toCharArray(total);
    }

    public static void main(String[] args) {
        //Add String iteratively
        WrappedList wrappedList = new WrappedList();
        wrappedList.add("back");
        wrappedList.add("pack");
        wrappedList.add("back1");
        wrappedList.add("pack1");
        final char[] charArray = wrappedList.toCharArray();
        System.out.println("Your char array:");
        for (char c : charArray) {
            System.out.println(c);
        }

        //Utility method one time for all, should by used in stand-alone Utility class
        System.out.println("As util method");
        System.out.println(wrappedList.toCharArray(wrappedList.getList()));
    }

}

See also: system-arraycopy-than-a-for-loop-for-copying-arrays

How to convert ArrayList of Strings to char array

5 Answers5